Types

Contents

1. Basic Data Types
2. Derived Data Types
3. User-Defined Types
4. Type Conversions
   1. Pointer Conversions
   2. Implicit Conversions
   3. Integer Promotions
   4. Usual Arithmetic Conversions
5. bool
6. Delegates
7. typeof
8. Mixin Types
9. Aliased Types
   1. size_t
   2. ptrdiff_t
   3. string

D is statically typed. Every expression has a type. Types constrain the values an expression can hold, and determine the semantics of operations on those values.

Type:
    TypeCtorsopt BasicType TypeSuffixesopt

TypeCtors:
    TypeCtor
    TypeCtor TypeCtors

TypeCtor:
    const
    immutable
    inout
    shared

BasicType:
    FundamentalType
    . QualifiedIdentifier
    QualifiedIdentifier
    Typeof
    Typeof . QualifiedIdentifier
    TypeCtor ( Type )
    Vector
    Traits
    MixinType

Vector:
    __vector ( VectorBaseType )

VectorBaseType:
    Type

FundamentalType:
    bool
    byte
    ubyte
    short
    ushort
    int
    uint
    long
    ulong
    cent
    ucent
    char
    wchar
    dchar
    float
    double
    real
    ifloat
    idouble
    ireal
    cfloat
    cdouble
    creal
    void

TypeSuffixes:
    TypeSuffix TypeSuffixesopt

TypeSuffix:
    *
    [ ]
    [ AssignExpression ]
    [ AssignExpression .. AssignExpression ]
    [ Type ]
    delegate Parameters MemberFunctionAttributesopt
    function Parameters FunctionAttributesopt

QualifiedIdentifier:
    Identifier
    Identifier . QualifiedIdentifier
    TemplateInstance
    TemplateInstance . QualifiedIdentifier
    Identifier [ AssignExpression ]
    Identifier [ AssignExpression ]. QualifiedIdentifier

Basic Data Types are leaf types. Derived Data Types build on leaf types. User-Defined Types are aggregates of basic and derived types.

Basic Data Types

Basic Data Types

Keyword	Default Initializer (.init)	Description
void	no default initializer	void has no value
bool	false	boolean value
byte	0	signed 8 bits
ubyte	0u	unsigned 8 bits
short	0	signed 16 bits
ushort	0u	unsigned 16 bits
int	0	signed 32 bits
uint	0u	unsigned 32 bits
long	0L	signed 64 bits
ulong	0uL	unsigned 64 bits
cent	0	signed 128 bits (reserved for future use)
ucent	0u	unsigned 128 bits (reserved for future use)
float	float.nan	32 bit floating point
double	double.nan	64 bit floating point
real	real.nan	largest floating point size available
ifloat	float.nan*1.0i	imaginary float
idouble	double.nan*1.0i	imaginary double
ireal	real.nan*1.0i	imaginary real
cfloat	float.nan+float.nan*1.0i	a complex number of two float values
cdouble	double.nan+double.nan*1.0i	complex double
creal	real.nan+real.nan*1.0i	complex real
char	'xFF'	unsigned 8 bit (UTF-8 code unit)
wchar	'uFFFF'	unsigned 16 bit (UTF-16 code unit)
dchar	'U0000FFFF'	unsigned 32 bit (UTF-32 code unit)

Implementation Defined: The real floating point type has at least the range and precision of the double type. On x86 CPUs it is often implemented as the 80 bit Extended Real type supported by the x86 FPU.

Derived Data Types

• Pointer
• Static Array
• Dynamic Array
• Associative Array
• Functions
• Delegates

User-Defined Types

• Enums
• Structs and Unions
• Classes
• Interfaces

Type Conversions

See also: CastExpression.

Pointer Conversions

Casting pointers to non-pointers and vice versa is allowed.

Best Practices: do not do this for any pointers that point to data allocated by the garbage collector.

Implicit Conversions

Implicit conversions are used to automatically convert types as required.

An enum can be implicitly converted to its base type, but going the other way requires an explicit conversion. For example:

int i;

enum Foo { E }
Foo f;
i = f;           // OK
f = i;           // error
f = cast(Foo)i;  // OK
f = 0;           // error
f = Foo.E;       // OK

A derived class can be implicitly converted to its base class, but going the other way requires an explicit cast. For example:

class Base {}
class Derived : Base {}
Base bd = new Derived();              // implicit conversion
Derived db = cast(Derived)new Base(); // explicit conversion

A dynamic array, say x, of a derived class can be implicitly converted to a dynamic array, say y, of a base class iff elements of x and y are qualified as being either both const or both immutable.

class Base {}
class Derived : Base {}
const(Base)[] ca = (const(Derived)[]).init; // `const` elements
immutable(Base)[] ia = (immutable(Derived)[]).init; // `immutable` elements

A static array, say x, of a derived class can be implicitly converted to a static array, say y, of a base class iff elements of x and y are qualified as being either both const or both immutable or both mutable (neither const nor immutable).

class Base {}
class Derived : Base {}
Base[3] ma = (Derived[3]).init; // mutable elements
const(Base)[3] ca = (const(Derived)[3]).init; // `const` elements
immutable(Base)[3] ia = (immutable(Derived)[3]).init; // `immutable` elements

Integer Promotions

Integer Promotions are conversions of the following types:

Integer Promotions

from	to
bool	int
byte	int
ubyte	int
short	int
ushort	int
char	int
wchar	int
dchar	uint

If an enum has as a base type one of the types in the left column, it is converted to the type in the right column.

Usual Arithmetic Conversions

The usual arithmetic conversions convert operands of binary operators to a common type. The operands must already be of arithmetic types. The following rules are applied in order, looking at the base type:

1. If either operand is real, the other operand is converted to real.
2. Else if either operand is double, the other operand is converted to double.
3. Else if either operand is float, the other operand is converted to float.
4. Else the integer promotions are done on each operand, followed by:
   1. If both are the same type, no more conversions are done.
   2. If both are signed or both are unsigned, the smaller type is converted to the larger.
   3. If the signed type is larger than the unsigned type, the unsigned type is converted to the signed type.
   4. The signed type is converted to the unsigned type.

If one or both of the operand types is an enum after undergoing the above conversions, the result type is:

1. If the operands are the same type, the result will be of that type.
2. If one operand is an enum and the other is the base type of that enum, the result is the base type.
3. If the two operands are different enums, the result is the closest base type common to both. A base type being closer means there is a shorter sequence of conversions to base type to get there from the original type.

Integer values cannot be implicitly converted to another type that cannot represent the integer bit pattern after integral promotion. For example:

ubyte  u1 = -1;       // error, -1 cannot be represented in a ubyte
ushort u2 = -1;       // error, -1 cannot be represented in a ushort
uint   u3 = int(-1);  // ok, -1 can be represented in a uint
ulong  u4 = long(-1); // ok, -1 can be represented in a ulong

Floating point types cannot be implicitly converted to integral types. Complex or imaginary floating point types cannot be implicitly converted to non-complex floating point types. Non-complex floating point types cannot be implicitly converted to imaginary floating point types.

bool

The bool type is a byte-size type that can only hold the value true or false.

The only operators that can accept operands of type bool are: & |, ^, &=, |=, ^=, !, &&, ||, and ?:.

A bool value can be implicitly converted to any integral type, with false becoming 0 and true becoming 1.

The numeric literals 0 and 1 can be implicitly converted to the bool values false and true, respectively. Casting an expression to bool means testing for 0 or !=0 for arithmetic types, and null or !=null for pointers or references.

Delegates

Delegates are an aggregate of two pieces of data: an object reference and a pointer to a non-static member function, or a pointer to a closure and a pointer to a nested function. The object reference forms the this pointer when the function is called.

Delegates are declared similarly to function pointers:

int function(int) fp; // fp is pointer to a function
int delegate(int) dg; // dg is a delegate to a function

A delegate is initialized analogously to function pointers:

int func(int);
fp = &func;   // fp points to func
class OB
{
    int member(int);
}
OB o;
dg = &o.member; // dg is a delegate to object o and
                // member function member

Delegates cannot be initialized with static member functions or non-member functions.

Delegates are called analogously to function pointers:

fp(3);   // call func(3)
dg(3);   // call o.member(3)

The equivalent of member function pointers can be constructed using anonymous lambda functions:

class C
{
    int a;
    int foo(int i) { return i + a; }
}

// mfp is the member function pointer
auto mfp = function(C self, int i) { return self.foo(i); };
auto c = new C();  // create an instance of C
mfp(c, 1);  // and call c.foo(1)

The C style syntax for declaring pointers to functions is deprecated:

int (*fp)(int);  // fp is pointer to a function

typeof

Typeof:
    typeof ( Expression )
    typeof ( return )

typeof is a way to specify a type based on the type of an expression. For example:

void func(int i)
{
    typeof(i) j;       // j is of type int
    typeof(3 + 6.0) x; // x is of type double
    typeof(1)* p;      // p is of type pointer to int
    int[typeof(p)] a;  // a is of type int[int*]

    writeln(typeof('c').sizeof); // prints 1
    double c = cast(typeof(1.0))j; // cast j to double
}

Expression is not evaluated, it is used purely to generate the type:

void func()
{
    int i = 1;
    typeof(++i) j; // j is declared to be an int, i is not incremented
    writeln(i);  // prints 1
}

Special cases:

1. typeof(this) will generate the type of what this would be in a non-static member function, even if not in a member function.
2. Analogously, typeof(super) will generate the type of what super would be in a non-static member function.
3. typeof(return) will, when inside a function scope, give the return type of that function.

class A { }

class B : A
{
    typeof(this) x;  // x is declared to be a B
    typeof(super) y; // y is declared to be an A
}

struct C
{
    static typeof(this) z;  // z is declared to be a C

    typeof(super) q; // error, no super struct for C
}

typeof(this) r;   // error, no enclosing struct or class

If the expression is a Property Function, typeof gives its return type.

struct S
{
    @property int foo() { return 1; }
}
typeof(S.foo) n;  // n is declared to be an int

Best Practices:

1. Typeof is most useful in writing generic template code.

Mixin Types

MixinType:
    mixin ( ArgumentList )

Each AssignExpression in the ArgumentList is evaluated at compile time, and the result must be representable as a string. The resulting strings are concatenated to form a string. The text contents of the string must be compilable as a valid Type, and is compiled as such.

void test(mixin("int")* p) // int* p
{
    mixin("int")[] a;      // int[] a;
    mixin("int[]") b;      // int[] b;
}

Aliased Types

size_t

size_t is an alias to one of the unsigned integral basic types, and represents a type that is large enough to represent an offset into all addressable memory.

ptrdiff_t

ptrdiff_t is an alias to the signed integral basic type the same size as size_t.

string

A string is a special case of an array.