On Thursday, November 10, 2011 03:34:07 Walter Bright wrote: > On 11/10/2011 2:00 AM, Russel Winder wrote: > > Purity is not really something I understand here without some lead in. > > I guess I failed to read part of Andrei's book ;-) > > A pure function in D is one that has no side effects. It is set by adding > the keyword "pure" to a function, and is checked by the compiler. > > A pure function may not modify any data reachable through its parameters, > may not read or write to any mutable global state, and can only call > functions that also are either pure or restrict the variables they modify > to those of the calling pure function's. > > A pure function may allocate data via new, and may throw an exception.
That's not really true anymore thanks to the distinction of strongly pure and weakly pure. It's true for strongly pure, but for pure as a whole, all it guarantees is that the function doesn't access any mutable global or static state and only calls functions which are pure. pure on its own makes _zero_ guarantees about the parameters. It's only when the parameters are immutable or implicitly convertible to immutable that anything about the parameters is guaranteed. - Jonathan M Davis
