Strange function argument name behaviour

Question

I asked a questions about cmake and passing variables here. I can make it work, but only if I name my variable in the function differently than the variable in parent scope I call the function for. So in essence:

function(strange name)
   message(STATUS ${name})
   message(STATUS ${${name}})
endfunction()

set(name foo)
set(anothername foo)
strange(name)
strange(anothername)

Which results in:

-- name   (message(STATUS ${name}) for var "name")
-- name   (message(STATUS ${${name}}) for var "name")
-- anothername message(STATUS ${name}) for var "anothername")
-- foo    (message(STATUS ${${name}}) for var "anothername")

Isn't that a little weird? What's happening? I think the behaviour of a function should not depend on the naming of variable in the parent scope - should it?!

Any clarification is much appreciated!

Lindydancer · Accepted Answer · 2013-01-18 11:22:58Z

8

Unfortunately, the language of CMake is extremely primitive. In this case, the naming of local variables may interact with variables with the same name in outer scopes.

Concretely, in the two calls ${${name}} expands to ${name} and ${anothername}, respectively. In the former name is the name of a local variable whose value is used. In the latter, the anothername from the outer scope is used.

I don't know of any way around this, except using obfuscated variable names in function accept variable names as arguments.

Maybe we should petition for a ${name:PARENT_SCOPE} from the CMake team?

answered Jan 18, 2013 at 11:22

Lindydancer

26.3k4 gold badges54 silver badges72 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Fraser Over a year ago

+1 for a clear answer. Not sure I'd favour your petition though :-) If anything, I'd prefer an AUTHOR_WARNING type message, warning about the local variable hiding the parent one.

Fraser · Accepted Answer · 2013-01-19 05:14:47Z

4

If you want to avoid the local scoping issues described in @Lindydancer's concise answer, you can change your function to a macro

From the documentation of macro:

Note that the parameters to a macro and values such as ARGN are not variables in the usual CMake sense. They are string replacements much like the c preprocessor would do with a macro. If you want true CMake variables you should look at the function command.

If you change to use macro, your output becomes

-- name
-- foo
-- anothername
-- foo

answered Jan 19, 2013 at 5:14

Fraser

79k23 gold badges255 silver badges225 bronze badges

2 Comments

nandaloo Over a year ago

Thanks for that additional information. Though, I wonder what the advantage of a function over a macro is at all then...

Fraser Over a year ago

I usually prefer a function as it doesn't "pollute" the parent namespace with variables used only in the function.

Collectives™ on Stack Overflow

Strange function argument name behaviour

2 Answers 2

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related