Proposal: .isizeof property for compile-time instance size

[Sean Kelly]

(this was originally posted to D bugs, but turned out to be a mistake so 
I'm reposting it here for discussion)

As D lacks a lexical specifier for class reference types there is 
currently no way to determine the size of a class instance at 
compile-time.  A simple solution would be to add a new property, valid 
for pointer and reference types, that evaluates to the size of the 
referenced type.  Thus:

(byte*).isizeof == byte.sizeof == 1
(byte**).isizeof == (byte*).sizeof == 4 (on 32-bit systems)
byte.isizeof == Error: property isizeof is only valid for reference types.

MyClass { int x, y; }
MyClass.isizeof == 8
(MyClass*).isizeof == MyClass.sizeof == 4 (on 32-bit systems)

Multiple levels of indirection can be eliminated using recursive 
templates, so there is no reason to collapse multiple levels of 
indirection and return the size of the final referenced type.