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test_inline_switch.zig (1111B) - Raw

      1 const std = @import("std");
      2 const expect = std.testing.expect;
      3 const expectError = std.testing.expectError;
      4 
      5 fn isFieldOptional(comptime T: type, field_index: usize) !bool {
      6     const fields = @typeInfo(T).@"struct".fields;
      7     return switch (field_index) {
      8         // This prong is analyzed twice with `idx` being a
      9         // comptime-known value each time.
     10         inline 0, 1 => |idx| @typeInfo(fields[idx].type) == .optional,
     11         else => return error.IndexOutOfBounds,
     12     };
     13 }
     14 
     15 const Struct1 = struct { a: u32, b: ?u32 };
     16 
     17 test "using @typeInfo with runtime values" {
     18     var index: usize = 0;
     19     try expect(!try isFieldOptional(Struct1, index));
     20     index += 1;
     21     try expect(try isFieldOptional(Struct1, index));
     22     index += 1;
     23     try expectError(error.IndexOutOfBounds, isFieldOptional(Struct1, index));
     24 }
     25 
     26 // Calls to `isFieldOptional` on `Struct1` get unrolled to an equivalent
     27 // of this function:
     28 fn isFieldOptionalUnrolled(field_index: usize) !bool {
     29     return switch (field_index) {
     30         0 => false,
     31         1 => true,
     32         else => return error.IndexOutOfBounds,
     33     };
     34 }
     35 
     36 // test