Purity (D2 standard libraries / object.d)

[Walter Bright]

Andrei Alexandrescu wrote:
> Walter Bright wrote:
>> Michel Fortin wrote:
>>> Hum, could the compiler be trusted to add the memoization code to 
>>> pure functions so they can stay pure?
>>
>> If the compiler does general memoization on pure functions, all it has 
>> to do is use the bits of the arguments passed on the stack to the 
>> function as an index into an associative array of the return values.
> 
> Not the bits, the full objects if they have indirection. (Pure functions 
> should accept const parameters!)

You're right, the "just the bits on the stack" is if the arguments are 
immutable. Const arguments would have to include whatever was indirectly 
referenced, which I argue is impractical for the runtime to handle 
automatically.