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Random.array: use sliceAsBytes #35687

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Fixes #35683

Fixes #35683
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I believe this could cause weird behaviour if E is not an integer type.
For example, if E is enum (u2) { A, B, C } then it'd be possible to get an integer value of 3 which isn't mapped to an actual value.
Random.array could just be restricted to integer types, but it'd also be nice to have it be able to generate arrays of enums, though in that case it'd likely have to do

for(result)|*e|{e.*=r.enumValue(E);}

for all enums which don't have a value associated with every single integer representation, which could be rather slow.

I believe this could cause weird behaviour if `E` is not an integer type. For example, if `E` is `enum (u2) { A, B, C }` then it'd be possible to get an integer value of `3` which isn't mapped to an actual value. `Random.array` could just be restricted to integer types, but it'd also be nice to have it be able to generate arrays of enums, though in that case it'd likely have to do ```zig for (result) |*e| { e.* = r.enumValue(E); } ``` for all enums which don't have a value associated with every single integer representation, which could be rather slow.
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Random.array could just be restricted to integer types

this is the right way

generate arrays of enums

this should be implemented in the userspace

> `Random.array` could just be restricted to integer types this is the right way > generate arrays of enums this should be implemented in the userspace
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there can be one branch that checks std.meta.hasUniqueRepresentation(E) and uses the code as is in the current PR
the else branch can use a loop

there can be one branch that checks `std.meta.hasUniqueRepresentation(E)` and uses the code as is in the current PR the else branch can use a loop
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@nektro wrote in #35687 (comment):

there can be one branch that checks std.meta.hasUniqueRepresentation(E) and uses the code as is in the current PR the else branch can use a loop

This sounds like a good solution, I'll have to find all the possible types for the else branch

@nektro wrote in https://codeberg.org/ziglang/zig/pulls/35687#issuecomment-17156045: > there can be one branch that checks `std.meta.hasUniqueRepresentation(E)` and uses the code as is in the current PR the else branch can use a loop This sounds like a good solution, I'll have to find all the possible types for the else branch
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i meant a literal else branch similar to this

pubfnarray(r:Random,comptimeE:type,comptimeN:usize)[N]E{varresult:[N]E=undefined;if(std.meta.hasUniqueRepresentation(E)){bytes(r,std.mem.sliceAsBytes(&result));}else{for(&result)|*item|item.*=@bitCast(int(r,@Int(.unsigned,@bitSizeOf(E))));}returnresult;}
i meant a literal else branch similar to this ```zig pub fn array(r: Random, comptime E: type, comptime N: usize) [N]E { var result: [N]E = undefined; if (std.meta.hasUniqueRepresentation(E)) { bytes(r, std.mem.sliceAsBytes(&result)); } else { for (&result) |*item| item.* = @bitCast(int(r, @Int(.unsigned, @bitSizeOf(E)))); } return result; } ```
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That wouldn't solve the issue of invalid enum values for exhaustive enums

That wouldn't solve the issue of invalid enum values for exhaustive enums
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although in hindsight that also wouldnt be perfect because enum { a, b, c, d, e } would be backed by u3 but have many invalid values like Rue pointed out so you may need to check typeInfo and use .enumValue(E) for example, but the use of the if statement stands

although in hindsight that also wouldnt be perfect because `enum { a, b, c, d, e }` would be backed by `u3` but have many invalid values like Rue pointed out so you may need to check typeInfo and use `.enumValue(E)` for example, but the use of the if statement stands
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I was thinking something more like

pubfnarray(r:Random,comptimeE:type,comptimeN:usize)[N]E{varresult:[N]E=undefined;if(std.meta.hasUniqueRepresentation(E)){bytes(r,std.mem.sliceAsBytes(&result));}else{for(&result)|*val|{val.*=switch(@typeInfo(E)){.@"enum"=>r.enumValue(E),.int=>r.int(E),.float=>r.float(E),else=>@compileError("Type"++@typeName(E)++" not supported"),};}}returnresult;}
I was thinking something more like ```zig pub fn array(r: Random, comptime E: type, comptime N: usize) [N]E { var result: [N]E = undefined; if (std.meta.hasUniqueRepresentation(E)) { bytes(r, std.mem.sliceAsBytes(&result)); } else { for (&result) |*val| { val.* = switch (@typeInfo(E)) { .@"enum" => r.enumValue(E), .int => r.int(E), .float => r.float(E), else => @compileError("Type" ++ @typeName(E) ++ " not supported"), }; } } return result; } ```
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I believe that in a case like that it'd make more sense to have to switch based on E outside and then hasUniqueRepresentation check inside, because with the code you have there, if E == f32 it'd fill the array with values between 0.0 and 1.0, but if hasUniqueRepresentation gets changed so it returns true for f32, that'd also change the behaviour of array(f32, ...). I doubt the person changing hasUniqueRepresentation would notice that change in behaviour, and we'd probably end up with some confused users of array(f32, ...).

I believe that in a case like that it'd make more sense to have to switch based on `E` outside and then `hasUniqueRepresentation` check inside, because with the code you have there, if `E == f32` it'd fill the array with values between `0.0` and `1.0`, but if `hasUniqueRepresentation` gets changed so it returns `true` for `f32`, that'd also change the behaviour of `array(f32, ...)`. I doubt the person changing `hasUniqueRepresentation` would notice that change in behaviour, and we'd probably end up with some confused users of `array(f32, ...)`.
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Unit test coverage please, doesn't have to be fancy.

Unit test coverage please, doesn't have to be fancy.
@ -76,3 +76,3 @@
pubfnarray(r:Random,comptimeE:type,comptimeN:usize)[N]E{
varresult:[N]E=undefined;
bytes(r,&result);
bytes(r,std.mem.sliceAsBytes(&result));
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- bytes(r, std.mem.sliceAsBytes(&result));
+ bytes(r, @ptrCast(&result));
```diff - bytes(r, std.mem.sliceAsBytes(&result)); + bytes(r, @ptrCast(&result)); ```
Der_Teufel marked this conversation as resolved
Der_Teufel force-pushed fix-random-array from 8b0e88be64
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2026年06月13日 12:37:29 +02:00 Compare
Add a test for Random.array to make sure it compiles
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d665a6f132
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I did a basic test here: gschwind/zig@8a928aa914

maybe you want to include it.

Best regards

I did a basic test here: https://codeberg.org/gschwind/zig/commit/8a928aa91475e2da77e72793033a165f598b98a3 maybe you want to include it. Best regards
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Just noticed that you did include test, you should add type that evaluate std.meta.hasUniqueRepresentation(E) to false.

Just noticed that you did include test, you should add type that evaluate `std.meta.hasUniqueRepresentation(E)` to false.
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