Question

Why are warnings generated when calling methods undeclared in a class interface using conventional means, but not when calling methods using @selector? Is it because selectors can be executed by a different caller than self?

For example:

-(void) doStuff
{
    [self doNow]; // Warning: instance method not found
    SEL sel = @selector(doNow); // no warnings
}   

-(void) doNow {} // this method is not declared in the interface

Answer 1

The “Undeclared Selector” warning is turned off by default. I don’t know why. You can turn it back on in the Build Settings.

The documentation for this settings reads:

Warn if a “@selector(…)” expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the “@selector(…)” expression, either explicitly in an @interface or @protocol declaration, or implicitly in an @implementation section. This option always performs its checks as soon as a “@selector(…)” expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used. [GCC_WARN_UNDECLARED_SELECTOR, -Wundeclared-selector]