Bug 23361 – std.uni.normalize should be pure

----------- @safe pure auto fun() { import std.uni; return "a\u0308".normalize; } ----------- Errors, with both nightly and stable DMD: onlineapp.d(3): Error: `pure` function `onlineapp.fun` cannot call impure function `std.uni.normalize!(NormalizationForm.NFC, char).normalize` There is nothing in `normalize` that should alter global state, so this should compile. I'm classifying this as major, because this is the only way to normalize Unicode strings in D without a DIY or third-party library. The function not being available in pure code is a serious hinderance.

I took a look at this. If you mark the following as pure: normalize decompose decomposeHangul Then there's only this that needs to be pure (in normalize) () @trusted { decomposed.assumeSafeAppend(); ccc.length = 0; ccc.assumeSafeAppend(); } (); To cheat and not make the appenders pure but the block pure we can just add pure: () @trusted pure { decomposed.assumeSafeAppend(); ccc.length = 0; ccc.assumeSafeAppend(); } (); But, we still need some way there to allow calling the impure append from the pure block. Maybe we could cast some function pointer to pure, I don't know. I tested wrapping it in a debug block and that makes it work, but I'm not sure what the "real" solution would look like. () @trusted pure { debug { decomposed.assumeSafeAppend(); ccc.length = 0; ccc.assumeSafeAppend(); } } ();

One way I guess is to cast the function to pure. The other is to actually mark _d_arrayshrinkfit as pure. Which of those seems most reasonable?

@dukc created dlang/phobos pull request #8763 "fix issue 23361 - std.uni.normalize made pure" fixing this issue: - fix issue 23361 - std.uni.normalize made pure https://github.com/dlang/phobos/pull/8763

Oh, it seems I have missed your comment - I just figured all this out myself creating a fix for this when I could just have read your message. I solved the assumeSafeAppend thing by marking the calls pure. (But with a cast - does simply marking the lambda pure really work? I thought even `@trusted` code lets to treat impure calls as pure only with an explicit cast.) I think it's okay because... well let me copy my comment from the code as explaination: --- // assumeSafeAppend isn't considered pure as of writing, hence the // cast. It isn't pure in the sense that the elements after // the array in question are affected, but we don't use those // making the call pure for our purposes. ---

dlang/phobos pull request #8763 "fix issue 23361 - std.uni.normalize made pure" was merged into master: - e6ed40182187ea4f3caf1127102136f9aa5fd0ac by Ate Eskola: fix issue 23361 - std.uni.normalize made pure https://github.com/dlang/phobos/pull/8763