[Cmake] Substitution or not between quotes?

[Brad King]

Martin Trudeau wrote:
> Hi.
> 
> Could anyone explain to me why
> 
> #################
> IF("y" MATCHES "^y$")
> MESSAGE("match")
> ELSE("y" MATCHES "^y$")
> MESSAGE("no match")
> ENDIF("y" MATCHES "^y$")
> ###################
> 
> produces the message "match" if y is not defined
> but "no match" if it is. I thought there was never any
> substitution taking place for strings between quotes, unless
> ${...} was used. So, if there is substitution, why and how?

The IF command has a special case for backward compatibility with very 
early CMake versions.  It allows the following to work:

IF(CMAKE_SOME_VAR MATCHES "^regex$")
ENDIF(CMAKE_SOME_VAR MATCHES "^regex$")

This is testing whether the contents of the variable CMAKE_SOME_VAR 
match the regular expression.  The behavior is documented here:

http://www.cmake.org/HTML/Documentation.html

The presence of the quotes in the first argument of an IF command has no 
effect unless a ${...} is present.

-Brad