Memory allocation purity

[w0rp via Digitalmars-d]

Ola, you do not understand 'pure.'

To consider the design of pure, you must first consider that you 
cannot add functional purity to an imperative language. It cannot 
be done. What you can do instead is what D offers with a 'weak 
purity' guarantee. That global state is not modified indirectly, 
that side-effects do not occur in a function, except through the 
function's parameters, except for memory allocation. D allows you 
to come pretty close to strong purity when a function is marked 
pure, does not allocate memory inside it or through its 
arguments, and has only const or immutable arguments. The only 
way you can get a better purity guarantee than that is to use a 
functional programming language like Haskell.