Re: Keeping a mutable reference to a struct with immutable members

[pineapple via Digitalmars-d-learn]

On Sunday, 29 May 2016 at 19:52:37 UTC, Basile B. wrote:
Do yo have a simple, concise runnable example to show ?

This is the example I was using to test solutions, it's similar 
to where I encountered the problem in the first place

    import core.stdc.stdlib : malloc, free;
    import std.stdio;
    import std.range;
    import std.traits;

    struct RepeatRange(Range) if(isForwardRange!Range){
        Range* source;
        Range original;

        this(Range original){
            this.original = original;
            this.repeat(original.save);
        }

        @property auto ref front(){
            return this.source.front;
        }
        void popFront(){
            this.source.popFront();
            if(this.source.empty) this.repeat(this.original.save);
        }

        @nogc void repeat(Range from){
            if(this.source) free(this.source);
            ubyte* newptr = cast(ubyte*) malloc(Range.sizeof);
            assert(newptr !is null, "Failed to allocate memory.");

            ubyte* fromptr = cast(ubyte*) &from;
            for(size_t i; i < Range.sizeof; i++) newptr[i] = 
fromptr[i];
            this.source = cast(Range*) newptr;
        }

        this(this){
            auto source = *this.source;
            this.source = null;
            this.repeat(source);
        }
        ~this(){
            if(this.source) free(this.source);
        }

        enum bool empty = false;
    }

    struct SomeForwardRange{
        int value = 0;
        const int other = 1; // Immutable member

        enum bool empty = false;
        @property auto ref save(){
            return SomeForwardRange(this.value);
        }
        @property auto ref front(){
            return this.value;
        }
        void popFront(){
            this.value++;
        }
    }

    void main(){
        auto range = 
RepeatRange!SomeForwardRange(SomeForwardRange(0));
        foreach(item; range.take(10)){
            writeln(item);
        }
    }