End of Life Ruby 3.1 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →

instance method

Module#module_eval

mod.module_eval(string [, filename [, lineno]]) → obj

mod.module_eval {|mod| block } → obj

static VALUE
rb_mod_module_eval_internal(int argc, const VALUE *argv, VALUE mod)
{
    return specific_eval(argc, argv, mod, FALSE, RB_PASS_CALLED_KEYWORDS);
}

Evaluates the string or block in the context of mod, except that when a block is given, constant/class variable lookup is not affected. This can be used to add methods to a class. module_eval returns the result of evaluating its argument. The optional filename and lineno parameters set the text for error messages.

Example

class Thing
end
a = %q{def hello() "Hello there!" end}
Thing.module_eval(a)
puts Thing.new.hello()
Thing.module_eval("invalid code", "dummy", 123)

produces:

Hello there!
dummy:123:in `module_eval': undefined local variable
    or method `code' for Thing:Class

See also #method_undefined #module_exec #method_removed #module_function also in 4.1 · 4.0 · 3.4 · 3.3 · 3.2 · 3.0

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