Why C++ compiles slowly

[Steven Schveighoffer]

On Wed, 25 Aug 2010 11:36:24 -0400, Simen kjaeraas  
<simen.kjaras at gmail.com> wrote:

> Steven Schveighoffer <schveiguy at yahoo.com> wrote:
>
>>> Pure might be worth stuffing in the symbol name, as the compiler may
>>> optimize things differently for pure vs. non-pure(dirty?) code.
>>> E.g. the result of a large, pure function that takes a while to compute
>>> might be cached to prevent calling it twice.
>>
>> These are decisions made at the compilation stage, not the linking  
>> stage.
>
> Absolutely. Now, you compile your module that uses a pure function foo in
> another module, and the above optimization is used. Later, that module is
> changed, and foo is changed to depend on some global state, and is thus
> no longer pure. After compiling this one module, you link your project,
> and the cached value is wrong, and boom! Nasal demons.

You could say the same about just about any function.  Changing  
implementation can be a bad source of stale object errors, I've had it  
happen many times in C++ without pure involved at all.  Moral is, always  
recompile everything :)

My point is just that name mangling was done to allow overloaded functions  
of the same name be linked by a linker who doesn't understand  
overloading.  If pure functions cannot be overloaded on purity alone, then  
there's no reason to mangle purity into the symbol.

But it's a moot point, since purity *is* mangled into the symbol name.

-Steve