Bug 8743 – Add support for memoizing class methods

This was asked for here: http://stackoverflow.com/questions/12677498/how-do-i-use-std-functional-memoize-inside-a-class There could be use-cases for this even though methods usually depend on internal class state. Perhaps if the method was @pure it would be safe to use it. Anyway I have an experimental implementation: module test; import std.stdio; import std.traits; import std.typecons; import std.datetime; template isClassStruct(alias fun) { enum bool isClassStruct = (is(fun == class) || is(fun == struct)); } mixin template memoize(alias fun, uint maxSize = uint.max) if (isClassStruct!(__traits(parent, fun))) { ReturnType!fun opCall(ParameterTypeTuple!fun args) { static ReturnType!fun[Tuple!(typeof(args))] memo; auto t = tuple(args); auto p = t in memo; if (p) return *p; static if (maxSize != uint.max) { if (memo.length >= maxSize) memo = null; } mixin("auto r = this." ~ __traits(identifier, fun) ~ "(args);"); memo[t] = r; return r; } } class A { int slowFunc(int a, int b) { int result; foreach (_; 0 .. 1024) { result += a; result += b; } return result; } mixin memoize!slowFunc fastFunc; } enum CallCount = 2048; void main() { A a = new A; auto sw1 = StopWatch(AutoStart.yes); foreach (x; 0 .. CallCount) { a.slowFunc(100, 100); // 11232 usecs } sw1.stop(); writeln(sw1.peek.usecs); auto sw2 = StopWatch(AutoStart.yes); foreach (x; 0 .. CallCount) { a.fastFunc(100, 100); // 302 usecs } sw2.stop(); writeln(sw2.peek.usecs); }

Here's another one that has rehashing ability: http://dpaste.dzfl.pl/abb6086f But it comes with a runtime cost of a boolean check. I'd love to be able to make rehash a compile-time parameter, but I can't seem to make opCall work with it. Even if it did work I'd have to figure out a way to store the hash outside of the template since each template instance has it's own internal hash.

Ahh, I've got it! Templates have their own scope, so the hash can go outside: http://dpaste.dzfl.pl/4ba280c7

(In reply to comment #2) > Ahh, I've got it! Templates have their own scope, so the hash can go outside: > > http://dpaste.dzfl.pl/4ba280c7 I suggest to put a copy of it in Bugzilla (as attach or just pasting it here), so it's readable even if dpaste is down, or it deletes this paste, etc.

void rehash() { memo = null; } Maybe do you mean something like this? void rehash() { memo.rehash; } void clear() { memo = null; }

(In reply to comment #4) > void rehash() { memo = null; } > > Maybe do you mean something like this? > > void rehash() { memo.rehash; } > void clear() { memo = null; } Absolutely. I've used the wrong term here. Here's the snippet: module test; import std.stdio; import std.traits; import std.typecons; import std.datetime; template isClassStruct(alias fun) { enum bool isClassStruct = (is(fun == class) || is(fun == struct)); } mixin template memoize(alias fun, uint maxSize = uint.max) if (isClassStruct!(__traits(parent, fun))) { ReturnType!fun[Tuple!(ParameterTypeTuple!fun)] memo; void rehash() { memo.rehash(); } void clear() { memo = null; } ReturnType!fun opCall(ParameterTypeTuple!fun args) { auto t = tuple(args); auto p = t in memo; if (p) return *p; static if (maxSize != uint.max) { if (memo.length >= maxSize) memo = null; } mixin("auto r = this." ~ __traits(identifier, fun) ~ "(args);"); memo[t] = r; return r; } } class A { int field; int slowFunc(int a, int b) { int result; foreach (_; 0 .. 1024) { result += a; result += b; } return result + field; } mixin memoize!slowFunc fastFunc; } enum CallCount = 2048; void main() { A a = new A; int z = a.fastFunc(100, 100); writeln(z); a.field = 50; a.fastFunc.clear(); z = a.fastFunc(100, 100); writeln(z); }

(In reply to comment #5) > enum bool isClassStruct = (is(fun == class) || is(fun == struct)); No need for extra parentheses: enum bool isClassStruct = is(fun == class) || is(fun == struct); > void rehash() { memo.rehash(); } I think () aren't needed, even with -property. > int slowFunc(int a, int b) If the arguments are constant it doesn't work: int slowFunc(in int a, in int b) > mixin memoize!slowFunc fastFunc; This mixin template is useful. A disadvantage is that it doesn't follow the API (usage) of the Phobos memoize. So maybe it needs a different name, like memoizeMethod, or something.

(In reply to comment #6) > If the arguments are constant it doesn't work: > int slowFunc(in int a, in int b) Seems to be a new bug related to Tuple: Issue 8746

(In reply to comment #6) > This mixin template is useful. A disadvantage is that it doesn't follow the API > (usage) of the Phobos memoize. So maybe it needs a different name, like > memoizeMethod, or something. Yes. I couldn't make it have the same syntax because of the requirement of the `this` reference.

(In reply to comment #8) > (In reply to comment #6) > > This mixin template is useful. A disadvantage is that it doesn't follow the API > > (usage) of the Phobos memoize. So maybe it needs a different name, like > > memoizeMethod, or something. > > Yes. I couldn't make it have the same syntax because of the requirement of the > `this` reference. Also I'm unsure about recursive calls. Existing memoize allows you to recursively call a memoized function.

(In reply to comment #9) > (In reply to comment #8) > > (In reply to comment #6) > > > This mixin template is useful. A disadvantage is that it doesn't follow the API > > > (usage) of the Phobos memoize. So maybe it needs a different name, like > > > memoizeMethod, or something. > > > > Yes. I couldn't make it have the same syntax because of the requirement of the > > `this` reference. > > Also I'm unsure about recursive calls. And I think I've uncovered yet another bug: class A { int slowFunc(int a, int b) { int result; /* Error: function expected before (), not mixin memoize!(slowFunc) fastFunc; */ if (a > 1) return fastFunc(a-1, b); return result; } mixin memoize!slowFunc fastFunc; } If I replace 'return fastFunc(a-1, b);' with 'return this.fastFunc(a-1, b)' it works.

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