class Binding
Objects of class Binding
encapsulate the execution context at some particular place in the code and retain this context for future use. The variables, methods, value of self
, and possibly an iterator block that can be accessed in this context are all retained. Binding objects can be created using Kernel#binding
, and are made available to the callback of Kernel#set_trace_func
.
These binding objects can be passed as the second argument of the Kernel#eval
method, establishing an environment for the evaluation.
class Demo def initialize(n) @secret = n end def get_binding binding end end k1 = Demo.new(99) b1 = k1.get_binding k2 = Demo.new(-3) b2 = k2.get_binding eval("@secret", b1) #=> 99 eval("@secret", b2) #=> -3 eval("@secret") #=> nil
Binding objects have no class-specific methods.
Public Instance Methods
static VALUE bind_eval(int argc, VALUE *argv, VALUE bindval) { VALUE args[4]; rb_scan_args(argc, argv, "12", &args[0], &args[2], &args[3]); args[1] = bindval; return rb_f_eval(argc+1, args, Qnil /* self will be searched in eval */); }
Evaluates the Ruby expression(s) in string, in the binding's context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.
def get_binding(param) binding end b = get_binding("hello") b.eval("param") #=> "hello"
static VALUE bind_local_variable_defined_p(VALUE bindval, VALUE sym) { ID lid = check_local_id(bindval, &sym); const rb_binding_t *bind; const rb_env_t *env; if (!lid) return Qfalse; GetBindingPtr(bindval, bind); env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)); return get_local_variable_ptr(&env, lid) ? Qtrue : Qfalse; }
Returns true
if a local variable symbol
exists.
def foo a = 1 binding.local_variable_defined?(:a) #=> true binding.local_variable_defined?(:b) #=> false end
This method is the short version of the following code:
binding.eval("defined?(#{symbol}) == 'local-variable'")
static VALUE bind_local_variable_get(VALUE bindval, VALUE sym) { ID lid = check_local_id(bindval, &sym); const rb_binding_t *bind; const VALUE *ptr; const rb_env_t *env; if (!lid) goto undefined; GetBindingPtr(bindval, bind); env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)); if ((ptr = get_local_variable_ptr(&env, lid)) == NULL) { sym = ID2SYM(lid); undefined: rb_name_err_raise("local variable `%1$s' not defined for %2$s", bindval, sym); } return *ptr; }
Returns the value of the local variable symbol
.
def foo a = 1 binding.local_variable_get(:a) #=> 1 binding.local_variable_get(:b) #=> NameError end
This method is the short version of the following code:
binding.eval("#{symbol}")
static VALUE bind_local_variable_set(VALUE bindval, VALUE sym, VALUE val) { ID lid = check_local_id(bindval, &sym); rb_binding_t *bind; const VALUE *ptr; const rb_env_t *env; if (!lid) lid = rb_intern_str(sym); GetBindingPtr(bindval, bind); env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)); if ((ptr = get_local_variable_ptr(&env, lid)) == NULL) { /* not found. create new env */ ptr = rb_binding_add_dynavars(bind, 1, &lid); env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)); } RB_OBJ_WRITE(env, ptr, val); return val; }
Set local variable named symbol
as obj
.
def foo a = 1 bind = binding bind.local_variable_set(:a, 2) # set existing local variable `a' bind.local_variable_set(:b, 3) # create new local variable `b' # `b' exists only in binding p bind.local_variable_get(:a) #=> 2 p bind.local_variable_get(:b) #=> 3 p a #=> 2 p b #=> NameError end
This method behaves similarly to the following code:
binding.eval("#{symbol} = #{obj}")
if obj
can be dumped in Ruby code.
static VALUE bind_local_variables(VALUE bindval) { const rb_binding_t *bind; const rb_env_t *env; GetBindingPtr(bindval, bind); env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block)); return rb_vm_env_local_variables(env); }
Returns the names of the binding's local variables as symbols.
def foo a = 1 2.times do |n| binding.local_variables #=> [:a, :n] end end
This method is the short version of the following code:
binding.eval("local_variables")
static VALUE bind_receiver(VALUE bindval) { const rb_binding_t *bind; GetBindingPtr(bindval, bind); return vm_block_self(&bind->block); }
Returns the bound receiver of the binding object.
Ruby Core © 1993–2017 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.