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Using a 2d-array lookup table produces error: runtime value contains reference to comptime var #25319
Description
Zig Version
0.16.0-dev.362+010d9a63f
Steps to Reproduce and Observed Behavior
Try to run the following code snippet:
pub fn main() void {
comptime var lookupTable: [32][32]u8 = @splat(@splat(0));
_ = &lookupTable;
var runtimeValue: usize = 0;
_ = &runtimeValue;
_ = lookupTable[runtimeValue][runtimeValue];
}Observe that it produces a compiler error:
$ zig-debug run test.zig
test.zig:10:17: error: runtime value contains reference to comptime var
_ = lookupTable[runtimeValue][runtimeValue];
~~~~~~~~~~~^~~~~~~~~~~~~~
test.zig:10:17: note: comptime var pointers are not available at runtime
test.zig:4:11: note: 'runtime_value' points to comptime var declared here
comptime var lookupTable: [32][32]u8 = @splat(@splat(0));
~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
referenced by:
callMain [inlined]: /home/mint/zig/zig-out/lib/zig/std/start.zig:618:22
callMainWithArgs [inlined]: /home/mint/zig/zig-out/lib/zig/std/start.zig:587:20
posixCallMainAndExit: /home/mint/zig/zig-out/lib/zig/std/start.zig:542:36
2 reference(s) hidden; use '-freference-trace=5' to see all references
This does not happen with one-dimensional arrays.
Expected Behavior
It used to work in older zig versions (0.16.0-dev.321+3cc0fc601), so I assume this regressed in #25154.
I assume it was an unintentional change, since it wasn't mentioned in the migration guide.
Activity
xdBronch commentedon Sep 21, 2025
i do believe this is intentional, it was mentioned in the original pr #25138 (comment)
in essence, these pieces of code are equivalent
this should definitely be mentioned in the upgrade guide
this i am not sure of though, that part may be a bug?