Re: Difference between slice[] and slice
On 25.09.19 22:36, WhatMeWorry wrote: On Wednesday, 25 September 2019 at 19:25:06 UTC, Ali Çehreli wrote: On 09/25/2019 12:06 PM, WhatMeWorry wrote: [...] > In short, is there anytime that one would want to use "slice[] = > something" syntax?I That changes element values. Ok. But which element(s)? All of them. For example, `slice[] = 42;` sets all elements to 42. And `slice[] = another_slice[];` replaces all elements of `slice` with copies of `another_slice`'s elements. In my specific case, I was using []. Is waste[] = waste[0..$-1]; even semantically meaningful? Because the LDC compiler had no problem compiling it. It's equivalent to this: waste[0] = waste[0..$-1][0]; waste[1] = waste[0..$-1][1]; ... waste[waste.length - 2] = waste[0..$-1][waste.length - 2]; waste[waste.length - 1] = waste[0..$-1][waste.length - 1]; So it basically does nothing. It just copies `waste`'s elements over themselves. Except that the last line makes an out-of-bounds access. That's an error that may be detected during compilation or at run time. Or if you're telling the compiler to optimize too aggressively, it might go unnoticed.
Re: Difference between slice[] and slice
On Wednesday, 25 September 2019 at 20:36:47 UTC, WhatMeWorry wrote: Ok. But which element(s)? In my specific case, I was using []. Is waste[] = waste[0..$-1]; even semantically meaningful? Because the LDC compiler had no problem compiling it. `waste[]` is just shorthand for `waste[0..$]`. Assigning to a slice means copying the contents of another array into the array that slice refers to. If the lengths of the source and destination don't match, you get an error. Since `waste[0..$]` and `waste[0..$-1]` can never have the same length, you will always get an error if you try to assign one to the other. Source: https://dlang.org/spec/arrays.html#array-copying
Re: Difference between slice[] and slice
On Wednesday, 25 September 2019 at 19:25:06 UTC, Ali Çehreli wrote: On 09/25/2019 12:06 PM, WhatMeWorry wrote: > I was > assuming that [] meant "the entirety" of the array. Assuming we're talking about D slices, Yes. (It could be a user-defined type with surprisingly different semantics.) > In short, is there anytime that one would want to use "slice[] = > something" syntax?I That changes element values. Ok. But which element(s)? In my specific case, I was using []. Is waste[] = waste[0..$-1]; even semantically meaningful? Because the LDC compiler had no problem compiling it. > //waste[] = waste[0..$-1]; // object.Error@(0): Array lengths don't > match for copy: 0 != 1 > > waste = waste[0..$-1]; // works That makes slice refer to a different set of elements. In that example, the slice does not include the last element anymore. Ali
Re: Difference between slice[] and slice
On 09/25/2019 12:06 PM, WhatMeWorry wrote: > I was > assuming that [] meant "the entirety" of the array. Assuming we're talking about D slices, Yes. (It could be a user-defined type with surprisingly different semantics.) > In short, is there anytime that one would want to use "slice[] = > something" syntax?I That changes element values. > //waste[] = waste[0..$-1]; // object.Error@(0): Array lengths don't > match for copy: 0 != 1 > > waste = waste[0..$-1]; // works That makes slice refer to a different set of elements. In that example, the slice does not include the last element anymore. Ali
Difference between slice[] and slice
Just got through debugging a line of code which uses dynamic array. It boiled to to my use of []. How should I "D think" about slice[]? The run time error seems to say the the length of [] is zero. I was assuming that [] meant "the entirety" of the array. In short, is there anytime that one would want to use "slice[] = something" syntax?I //waste[] = waste[0..$-1]; // object.Error@(0): Array lengths don't match for copy: 0 != 1 waste = waste[0..$-1]; // works
