instance method · added in Ruby 4.0

Binding#implicit_parameter_defined?

binding.implicit_parameter_defined?(symbol) → obj

static VALUE
bind_implicit_parameter_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 == idIt) lid = idItImplicit;

    if (!lid || !rb_implicit_param_p(lid)) {
        rb_name_err_raise("'%1$s' is not an implicit parameter",
                          bindval, sym);
    }

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    return RBOOL(get_local_variable_ptr(&env, lid, FALSE));
}

Returns true if the numbered parameter or “it” parameter exists.

Example

def foo
  [42].each do
    it
    binding.implicit_parameter_defined?(:it) #=> true
    binding.implicit_parameter_defined?(:_1) #=> false
  end

  { k: 42 }.each do
    _2
    binding.implicit_parameter_defined?(:_1) #=> true
    binding.implicit_parameter_defined?(:_2) #=> true
    binding.implicit_parameter_defined?(:_3) #=> false
    binding.implicit_parameter_defined?(:it) #=> false
  end
end

Ruby version changes

4.0
- Binding#implicit_parameters, Binding#implicit_parameter_get, and Binding#implicit_parameter_defined? have been added to access numbered parameters and “it” parameter. [Bug #21049]

See also #eval #implicit_parameter_get #implicit_parameters also in 4.1

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