Kernel#block_given?

block_given? → true or false

static VALUE
rb_f_block_given_p(VALUE _)
{
    rb_execution_context_t *ec = GET_EC();
    rb_control_frame_t *cfp = ec->cfp;
    cfp = vm_get_ruby_level_caller_cfp(ec, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));

    return RBOOL(cfp != NULL && VM_CF_BLOCK_HANDLER(cfp) != VM_BLOCK_HANDLER_NONE);
}

Returns true if yield would execute a block in the current context. The iterator? form is mildly deprecated.

Example

def try
  if block_given?
    yield
  else
    "no block"
  end
end
try                  #=> "no block"
try { "hello" }      #=> "hello"
try do "hello" end   #=> "hello"

See also #binding #callcc #BigDecimal #__callee__ also in 4.1 · 4.0 · 3.4 · 3.2 · 3.1 · 3.0

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