On Saturday 20 November 2010 10:47:27 Kagamin wrote: > Jonathan M Davis Wrote: > > > Doesn't immutability imply static storage? I also thought, it's a way > > > to force CTFE. > > > > No. If it did, you couldn't initialize immutable stuff at runtime. > > Apparently, in the case of globals or member variables (which have to be > > initialized statically anyway), it does mean that they could be > > optimized out (e.g. there's an open bug report on the fact that > > immutable fields in structs don't take any space), but that's no the > > case for local variables which can be initialized at runtime. > > I see no difference. Both globals and locals can be initialized at runtime > and both can be static.
I'm talking about direct initialization. If you do immutable a = func(); in global scope, func() _must_ be callable at compile-time. If you do that at local scope, it will be done at runtime. If you declare a local variable as static, then it's in the same boat as a global variable because it _is_ a global variable as far as its lifetime goes, just not its scope. However, notice that both auto a = func(); const a = func(); would have to have func() be callable at compile time if a is a global variable, whereas for a non-static local, it would be done at runtime. In comparison, enum a = func(); _always_ must have func() be callable at compile-time. immutable says nothing about whether a variable's value must be known at compile time. And CTFE only kicks in when the compiler _must_ do the initialization at compile time. Also, immutable by itself says nothing about static storage. It either has to be a global variable or be marked with static. And I believe that marking a global variable as static is redundant just like marking a method as public when it is already in a public block is redundant. static in C meant something for global variables, but C doesn't use modules. - Jonathan M Davis
