Top Level Namespace

Returns the standard output of executing command in a subshell. Standard input, and error are inherited. The special $? variable is set to a Process::Status associated with this execution.

It is impossible to call this method with any regular call syntax. There is an associated literal type which calls the method with the literal content as command:

`echo hi`   # => "hi\n"
$?.success? # => true

See Command literals in the language reference.

Terminates execution immediately, printing message to STDERR and then calling exit(status).

Registers the given Proc for execution when the program exits. If multiple handlers are registered, they are executed in reverse order of registration.

def do_at_exit(str1)
  at_exit { print str1 }
end

at_exit { puts "cruel world" }
do_at_exit("goodbye ")
exit

Produces:

goodbye cruel world

The exit status code that will be returned by this program is passed to the block as its first argument. In case of any unhandled exception, it is passed as the second argument to the block, if the program terminates normally or exit(status) is called explicitly, then the second argument will be nil.

NOTE If at_exit is called inside an at_exit handler, it will be called right after the current at_exit handler ends, and then other handlers will be invoked.

Returns the current execution stack as an array containing strings usually in the form file:line:column or file:line:column in 'method'.

Terminates execution immediately, returning the given status code to the invoking environment.

Registered at_exit procs are executed.

Reads a line from STDIN.

See also: IO#gets.

Returns the instance size of the given class as number of bytes.

type must be a constant or typeof() expression. It cannot be evaluated at runtime.

instance_sizeof(String)    # => 16
instance_sizeof(Exception) # => 48

See sizeof for determining the size of value types.

NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.

Repeatedly executes the block.

loop do
  line = gets
  break unless line
  # ...
end

Main function that acts as C's main function. Invokes Crystal.main.

Can be redefined. See Crystal.main for examples.

Returns the byte offset of an instance variable in a struct or class type.

type must be a constant or typeof() expression. It cannot be evaluated at runtime. offset must be the name of an instance variable of type, prefixed by @, or the index of an element in a Tuple, starting from 0, if type is a Tuple.

offsetof(String, @bytesize)       # => 4
offsetof(Exception, @message)     # => 8
offsetof(Time, @location)         # => 16
offsetof({Int32, Int8, Int32}, 0) # => 0
offsetof({Int32, Int8, Int32}, 1) # => 4
offsetof({Int32, Int8, Int32}, 2) # => 8

NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.

Inspects object to STDOUT followed by a newline. Returns object.

See also: Object#inspect(io).

Inspects each object in objects to STDOUT, followed by a newline. Returns objects.

See also: Object#inspect(io).

Inspects objects to STDOUT, followed by a newline. Returns objects.

p foo: 23, bar: 42 # => {foo: 23, bar: 42}

See Object#inspect(io)

Returns a Pointer to the contents of a variable.

variable must be a variable (local, instance, class or library).

a = 1
ptr = pointerof(a)
ptr.value = 2

a # => 2

NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.

Pretty prints object to STDOUT followed by a newline. Returns object.

See also: Object#pretty_print(pp).

Pretty prints each object in objects to STDOUT, followed by a newline. Returns objects.

See also: Object#pretty_print(pp).

Pretty prints objects to STDOUT, followed by a newline. Returns objects.

p foo: 23, bar: 42 # => {foo: 23, bar: 42}

See Object#pretty_print(pp)

Prints objects to STDOUT and then invokes STDOUT.flush.

See also: IO#print.

Prints a formatted string to STDOUT.

For details on the format string, see sprintf.

Prints a formatted string to STDOUT.

For details on the format string, see sprintf.

Prints objects to STDOUT, each followed by a newline character unless the object is a String and already ends with a newline.

See also: IO#puts.

Raises the exception.

This will set the exception's callstack if it hasn't been already. Re-raising a previously caught exception won't replace the callstack.

Raises an Exception with the message.

See Random#rand(x).

See Random#rand.

Reads a line from STDIN.

See also: IO#read_line.

Returns the size of the given type as number of bytes.

type must be a constant or typeof() expression. It cannot be evaluated at runtime.

sizeof(Int32)        # => 4
sizeof(Int64)        # => 8
sizeof(typeof(true)) # => 1

For Reference types, the size is the same as the size of a pointer:

# On a 64 bits machine
sizeof(Pointer(Int32)) # => 8
sizeof(String)         # => 8

This is because a Reference's memory is allocated on the heap and a pointer to it is passed around. The size of a class on the heap can be determined using #instance_sizeof.

NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.

Blocks the current fiber for the specified number of seconds.

While this fiber is waiting this time, other ready-to-execute fibers might start their execution.

Blocks the current Fiber for the specified time span.

While this fiber is waiting this time, other ready-to-execute fibers might start their execution.

Blocks the current fiber forever.

Meanwhile, other ready-to-execute fibers might start their execution.

Spawns a new fiber.

The newly created fiber doesn't run as soon as spawned.

Example:

# Write "1" every 1 second and "2" every 2 seconds for 6 seconds.

ch = Channel(Nil).new

spawn do
  6.times do
    sleep 1
    puts 1
  end
  ch.send(nil)
end

spawn do
  3.times do
    sleep 2
    puts 2
  end
  ch.send(nil)
end

2.times { ch.receive }

Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.

Within the format string, any characters other than format specifiers (specifiers beginning with %) are copied to the result. The formatter supports positional format specifiers (%.1f), formatted substitution (%.1f) and plain substitution (%{name}).

Substitutions expect the first argument to be a Hash or NamedTuple to resolve substitution names. Positional specifiers correspond to the positional values in the method arguments, or the array supplied as first argument.

A simple format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.

%[flags][width][.precision]type

A formatted substitution is similar but after the percent sign follows the mandatory name of the substitution wrapped in angle brackets.

%<name>[flags][width][.precision]type

The field type controls how the corresponding argument value is to be interpreted, while the flags modify that interpretation.

The field type characters are:

Field | Integer Format
------+------------------------------------------------------------------
  b   | Formats argument as a binary number.
  d   | Formats argument as a decimal number.
  i   | Same as d.
  o   | Formats argument as an octal number.
  x   | Formats argument as a hexadecimal number using lowercase letters.
  X   | Same as x, but uses uppercase letters.

Field | Float Format
------+---------------------------------------------------------------
  e   | Formats floating point argument into exponential notation
      | with one digit before the decimal point as [-]d.dddddde[+-]dd.
      | The precision specifies the number of digits after the decimal
      | point (defaulting to six).
  E   | Equivalent to e, but uses an uppercase E to indicate
      | the exponent.
  f   | Formats floating point argument as [-]ddd.dddddd,
      | where the precision specifies the number of digits after
      | the decimal point.
  g   | Formats a floating point number using exponential form
      | if the exponent is less than -4 or greater than or
      | equal to the precision, or in dd.dddd form otherwise.
      | The precision specifies the number of significant digits.
  G   | Equivalent to g, but use an uppercase E in exponent form.
  a   | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
      | which consists of an optional sign, "0x", fraction part
      | as hexadecimal, "p", and exponential part as decimal.
  A   | Equivalent to a, but uses uppercase X and P.

Field | Other Format
------+------------------------------------------------------------
  c   | Argument is a single character itself.
  s   | Argument is a string to be substituted. If the format
      | sequence contains a precision, at most that many characters
      | will be copied.
  %   | A percent sign itself will be displayed. No argument taken.

Flags modify the behavior of the format specifiers:

Flag     | Applies to    | Meaning
---------+---------------+--------------------------------------------
space    | bdiouxX       | Add a leading space character to
         | aAeEfgG       | non-negative numbers.
         | (numeric fmt) | For o, x, X, b, use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+--------------------------------------------
+        | bdiouxX       | Add a leading plus sign to non-negative
         | aAeEfgG       | numbers.
         | (numeric fmt) | For o, x, X, b, use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+--------------------------------------------
-        | all           | Left-justify the result of this conversion.
---------+---------------+--------------------------------------------
0 (zero) | bdiouxX       | Pad with zeros, not spaces.
         | aAeEfgG       | For o, x, X, b, radix-1
         | (numeric fmt) | is used for negative numbers formatted as
         |               | complements.

Examples of flags:

Decimal number conversion:

sprintf "%d", 123  # => "123"
sprintf "%+d", 123 # => "+123"
sprintf "% d", 123 # => " 123"

Octal number conversion:

sprintf "%o", 123   # => "173"
sprintf "%+o", 123  # => "+173"
sprintf "%o", -123  # => "-173"
sprintf "%+o", -123 # => "-173"

Hexadecimal number conversion:

sprintf "%x", 123   # => "7b"
sprintf "%+x", 123  # => "+7b"
sprintf "%x", -123  # => "-7b"
sprintf "%+x", -123 # => "-7b"
sprintf "%#x", 0    # => "0"
sprintf "% x", 123  # => " 7b"
sprintf "% x", -123 # => "-7b"
sprintf "%X", 123   # => "7B"
sprintf "%#X", -123 # => "-7B"

Binary number conversion:

sprintf "%b", 123    # => "1111011"
sprintf "%+b", 123   # => "+1111011"
sprintf "%+b", -123  # => "-1111011"
sprintf "%b", -123   # => "-1111011"
sprintf "%#b", 0     # => "0"
sprintf "% b", 123   # => " 1111011"
sprintf "%+ b", 123  # => "+ 1111011"
sprintf "% b", -123  # => "-1111011"
sprintf "%+ b", -123 # => "-1111011"

Floating point conversion:

sprintf "%a", 123 # => "0x1.ecp+6"
sprintf "%A", 123 # => "0X1.ECP+6"

Exponential form conversion:

sprintf "%g", 123.4          # => "123.4"
sprintf "%g", 123.4567       # => "123.457"
sprintf "%20.8g", 1234.56789 # => "           1234.5679"
sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
sprintf "%20.8G", 123456789  # => "       1.2345679E+08"
sprintf "%20.8g", -123456789 # => "      -1.2345679e+08"
sprintf "%20.8G", -123456789 # => "      -1.2345679E+08"

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

sprintf "%20d", 123   # => "                 123"
sprintf "%+20d", 123  # => "                +123"
sprintf "%020d", 123  # => "00000000000000000123"
sprintf "%+020d", 123 # => "+0000000000000000123"
sprintf "% 020d", 123 # => " 0000000000000000123"
sprintf "%-20d", 123  # => "123                 "
sprintf "%-+20d", 123 # => "+123                "
sprintf "%- 20d", 123 # => " 123                "
sprintf "%020x", -123 # => "00000000000000000-7b"
sprintf "%020X", -123 # => "00000000000000000-7B"

For numeric fields, the precision controls the number of decimal places displayed.

For string fields, the precision determines the maximum number of characters to be copied from the string.

Examples of precisions:

Precision for d, o, x and b is minimum number of digits:

sprintf "%20.8d", 123   # => "                 123"
sprintf "%020.8d", 123  # => "00000000000000000123"
sprintf "%20.8o", 123   # => "                 173"
sprintf "%020.8o", 123  # => "00000000000000000173"
sprintf "%20.8x", 123   # => "                  7b"
sprintf "%020.8x", 123  # => "0000000000000000007b"
sprintf "%20.8b", 123   # => "             1111011"
sprintf "%20.8d", -123  # => "                -123"
sprintf "%020.8d", -123 # => "0000000000000000-123"
sprintf "%20.8o", -123  # => "                -173"
sprintf "%20.8x", -123  # => "                 -7b"
sprintf "%20.8b", -11   # => "               -1011"

Precision for e is number of digits after the decimal point:

sprintf "%20.8e", 1234.56789 # => "      1.23456789e+03"

Precision for f is number of digits after the decimal point:

sprintf "%20.8f", 1234.56789 # => "       1234.56789000"

Precision for g is number of significant digits:

sprintf "%20.8g", 1234.56789 # => "           1234.5679"
sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
sprintf "%-20.8g", 123456789 # => "1.2345679e+08       "

Precision for s is maximum number of characters:

sprintf "%20.8s", "string test" # => "            string t"

Additional examples:

sprintf "%d %04x", 123, 123             # => "123 007b"
sprintf "%08b '%4s'", 123, 123          # => "01111011 ' 123'"
sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23"

Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.

Within the format string, any characters other than format specifiers (specifiers beginning with %) are copied to the result. The formatter supports positional format specifiers (%.1f), formatted substitution (%.1f) and plain substitution (%{name}).

Substitutions expect the first argument to be a Hash or NamedTuple to resolve substitution names. Positional specifiers correspond to the positional values in the method arguments, or the array supplied as first argument.

A simple format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.

%[flags][width][.precision]type

A formatted substitution is similar but after the percent sign follows the mandatory name of the substitution wrapped in angle brackets.

%<name>[flags][width][.precision]type

The field type controls how the corresponding argument value is to be interpreted, while the flags modify that interpretation.

The field type characters are:

Field | Integer Format
------+------------------------------------------------------------------
  b   | Formats argument as a binary number.
  d   | Formats argument as a decimal number.
  i   | Same as d.
  o   | Formats argument as an octal number.
  x   | Formats argument as a hexadecimal number using lowercase letters.
  X   | Same as x, but uses uppercase letters.

Field | Float Format
------+---------------------------------------------------------------
  e   | Formats floating point argument into exponential notation
      | with one digit before the decimal point as [-]d.dddddde[+-]dd.
      | The precision specifies the number of digits after the decimal
      | point (defaulting to six).
  E   | Equivalent to e, but uses an uppercase E to indicate
      | the exponent.
  f   | Formats floating point argument as [-]ddd.dddddd,
      | where the precision specifies the number of digits after
      | the decimal point.
  g   | Formats a floating point number using exponential form
      | if the exponent is less than -4 or greater than or
      | equal to the precision, or in dd.dddd form otherwise.
      | The precision specifies the number of significant digits.
  G   | Equivalent to g, but use an uppercase E in exponent form.
  a   | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
      | which consists of an optional sign, "0x", fraction part
      | as hexadecimal, "p", and exponential part as decimal.
  A   | Equivalent to a, but uses uppercase X and P.

Field | Other Format
------+------------------------------------------------------------
  c   | Argument is a single character itself.
  s   | Argument is a string to be substituted. If the format
      | sequence contains a precision, at most that many characters
      | will be copied.
  %   | A percent sign itself will be displayed. No argument taken.

Flags modify the behavior of the format specifiers:

Flag     | Applies to    | Meaning
---------+---------------+--------------------------------------------
space    | bdiouxX       | Add a leading space character to
         | aAeEfgG       | non-negative numbers.
         | (numeric fmt) | For o, x, X, b, use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+--------------------------------------------
+        | bdiouxX       | Add a leading plus sign to non-negative
         | aAeEfgG       | numbers.
         | (numeric fmt) | For o, x, X, b, use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+--------------------------------------------
-        | all           | Left-justify the result of this conversion.
---------+---------------+--------------------------------------------
0 (zero) | bdiouxX       | Pad with zeros, not spaces.
         | aAeEfgG       | For o, x, X, b, radix-1
         | (numeric fmt) | is used for negative numbers formatted as
         |               | complements.

Examples of flags:

Decimal number conversion:

sprintf "%d", 123  # => "123"
sprintf "%+d", 123 # => "+123"
sprintf "% d", 123 # => " 123"

Octal number conversion:

sprintf "%o", 123   # => "173"
sprintf "%+o", 123  # => "+173"
sprintf "%o", -123  # => "-173"
sprintf "%+o", -123 # => "-173"

Hexadecimal number conversion:

sprintf "%x", 123   # => "7b"
sprintf "%+x", 123  # => "+7b"
sprintf "%x", -123  # => "-7b"
sprintf "%+x", -123 # => "-7b"
sprintf "%#x", 0    # => "0"
sprintf "% x", 123  # => " 7b"
sprintf "% x", -123 # => "-7b"
sprintf "%X", 123   # => "7B"
sprintf "%#X", -123 # => "-7B"

Binary number conversion:

sprintf "%b", 123    # => "1111011"
sprintf "%+b", 123   # => "+1111011"
sprintf "%+b", -123  # => "-1111011"
sprintf "%b", -123   # => "-1111011"
sprintf "%#b", 0     # => "0"
sprintf "% b", 123   # => " 1111011"
sprintf "%+ b", 123  # => "+ 1111011"
sprintf "% b", -123  # => "-1111011"
sprintf "%+ b", -123 # => "-1111011"

Floating point conversion:

sprintf "%a", 123 # => "0x1.ecp+6"
sprintf "%A", 123 # => "0X1.ECP+6"

Exponential form conversion:

sprintf "%g", 123.4          # => "123.4"
sprintf "%g", 123.4567       # => "123.457"
sprintf "%20.8g", 1234.56789 # => "           1234.5679"
sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
sprintf "%20.8G", 123456789  # => "       1.2345679E+08"
sprintf "%20.8g", -123456789 # => "      -1.2345679e+08"
sprintf "%20.8G", -123456789 # => "      -1.2345679E+08"

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

sprintf "%20d", 123   # => "                 123"
sprintf "%+20d", 123  # => "                +123"
sprintf "%020d", 123  # => "00000000000000000123"
sprintf "%+020d", 123 # => "+0000000000000000123"
sprintf "% 020d", 123 # => " 0000000000000000123"
sprintf "%-20d", 123  # => "123                 "
sprintf "%-+20d", 123 # => "+123                "
sprintf "%- 20d", 123 # => " 123                "
sprintf "%020x", -123 # => "00000000000000000-7b"
sprintf "%020X", -123 # => "00000000000000000-7B"

For numeric fields, the precision controls the number of decimal places displayed.

For string fields, the precision determines the maximum number of characters to be copied from the string.

Examples of precisions:

Precision for d, o, x and b is minimum number of digits:

sprintf "%20.8d", 123   # => "                 123"
sprintf "%020.8d", 123  # => "00000000000000000123"
sprintf "%20.8o", 123   # => "                 173"
sprintf "%020.8o", 123  # => "00000000000000000173"
sprintf "%20.8x", 123   # => "                  7b"
sprintf "%020.8x", 123  # => "0000000000000000007b"
sprintf "%20.8b", 123   # => "             1111011"
sprintf "%20.8d", -123  # => "                -123"
sprintf "%020.8d", -123 # => "0000000000000000-123"
sprintf "%20.8o", -123  # => "                -173"
sprintf "%20.8x", -123  # => "                 -7b"
sprintf "%20.8b", -11   # => "               -1011"

Precision for e is number of digits after the decimal point:

sprintf "%20.8e", 1234.56789 # => "      1.23456789e+03"

Precision for f is number of digits after the decimal point:

sprintf "%20.8f", 1234.56789 # => "       1234.56789000"

Precision for g is number of significant digits:

sprintf "%20.8g", 1234.56789 # => "           1234.5679"
sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
sprintf "%-20.8g", 123456789 # => "1.2345679e+08       "

Precision for s is maximum number of characters:

sprintf "%20.8s", "string test" # => "            string t"

Additional examples:

sprintf "%d %04x", 123, 123             # => "123 007b"
sprintf "%08b '%4s'", 123, 123          # => "01111011 ' 123'"
sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23"

Executes the given command in a subshell. Standard input, output and error are inherited. Returns true if the command gives zero exit code, false otherwise. The special $? variable is set to a Process::Status associated with this execution.

If command contains no spaces and args is given, it will become its argument list.

If command contains spaces and args is given, command must include "${@}" (including the quotes) to receive the argument list.

No shell interpretation is done in args.

Example:

system("echo *")

Produces:

LICENSE shard.yml Readme.md spec src

Timeout keyword for use in select.

select
when x = ch.receive
  puts "got #{x}"
when timeout(1.seconds)
  puts "timeout"
end

NOTE It won't trigger if the select has an else case (i.e.: a non-blocking select).

Returns the type of an expression.

typeof(1) # => Int32

It accepts multiple arguments, and the result is the union of the expression types:

typeof(1, "a", 'a') # => (Int32 | String | Char)

The expressions passed as arguments to typeof do not evaluate. The compiler only analyzes their return type.

NOTE This is a pseudo-method provided directly by the Crystal compiler. It cannot be redefined nor overridden.

Prints a series of expressions together with their inspected values. Useful for print style debugging.

a = 1
p! a # => "a # => 1"

p! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"

See also: p, Object#inspect.

Prints a series of expressions together with their pretty printed values. Useful for print style debugging.

a = 1
pp! a # => "a # => 1"

pp! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"

See also: pp, Object#pretty_inspect.

Defines a Struct with the given name and properties.

The generated struct has a constructor with the given properties in the same order as declared. The struct only provides getters, not setters, making it immutable by default.

The properties can be type declarations or assignments.

You can pass a block to this macro, that will be inserted inside the struct definition.

record Point, x : Int32, y : Int32

Point.new 1, 2 # => #<Point(@x=1, @y=2)>

An example with the block version:

record Person, first_name : String, last_name : String do
  def full_name
    "#{first_name} #{last_name}"
  end
end

person = Person.new "John", "Doe"
person.full_name # => "John Doe"

An example with type declarations and default values:

record Point, x : Int32 = 0, y : Int32 = 0

Point.new      # => #<Point(@x=0, @y=0)>
Point.new y: 2 # => #<Point(@x=0, @y=2)>

An example with assignments (in this case the compiler must be able to infer the types from the default values):

record Point, x = 0, y = 0

Point.new      # => #<Point(@x=0, @y=0)>
Point.new y: 2 # => #<Point(@x=0, @y=2)>

This macro also provides a copy_with method which returns a copy of the record with the provided properties altered.

record Point, x = 0, y = 0

p = Point.new y: 2 # => #<Point(@x=0, @y=2)>
p.copy_with x: 3   # => #<Point(@x=3, @y=2)>
p                  # => #<Point(@x=0, @y=2)>

Spawns a fiber by first creating a Proc, passing the call's expressions to it, and letting the Proc finally invoke the call.

Compare this:

i = 0
while i < 5
  spawn { print(i) }
  i += 1
end
Fiber.yield
# Output: 55555

To this:

i = 0
while i < 5
  spawn print(i)
  i += 1
end
Fiber.yield
# Output: 01234

This is because in the first case all spawned fibers refer to the same local variable, while in the second example copies of i are passed to a Proc that eventually invokes the call.