• Freddy (12/12) Nov 07 2014 Why is size_t an alias and not a typedef(or a struct that is not
• Jonathan Marler (14/26) Nov 07 2014 size_t is meant to have a range large enough to hold any offset

"Freddy" <Hexagonalstar64 gmail.com> writes:

Why is size_t an alias and not a typedef(or a struct that is not
implictly convertable)

----test.d
void main(){
      ulong a;
      size_t b=a;//only compiles on 64-bit
}
----
$ dmd -m64 test

$ dmd -m32 test
test.d(3): Error: cannot implicitly convert expression (a) of
type ulong to uint

"Jonathan Marler" <johnnymarler gmail.com> writes:

On Friday, 7 November 2014 at 21:05:52 UTC, Freddy wrote:
 Why is size_t an alias and not a typedef(or a struct that is not
 implictly convertable)

 ----test.d
 void main(){
      ulong a;
      size_t b=a;//only compiles on 64-bit
 }
 ----
 $ dmd -m64 test

 $ dmd -m32 test
 test.d(3): Error: cannot implicitly convert expression (a) of
 type ulong to uint

size_t is meant to have a range large enough to hold any offset 
to any pointer on your platform.  On 32 bit this is a 32 bit 
unsigned integer (uint) and on 64 bit it is a 64 bit unsigned 
integer (ulong).  So on 32 bit size_t is the same as uint and on 
64 bit it is the same as ulong.  So it makes sense that this 
doesn't compile on 64 bit systems.

I could see you making an argument that a ulong should never be 
implicitly converted to a size_t because that could produce 
different results depending on the platform, but I don't think 
that if size_t is 32 bits that ulong should ever be implicitly 
converted to a size_t.  If you want to do something like that you 
better know what your doing and requiring an explicit cast is a 
reasonable way to protect against unsafe casts.