Zig Tutorial #5 — Type Conversion

I met some issues in conversion between integer and float and here are the summary I got from some experiments in case you have the same problem.

First, the easy one:

pub fn main() anyerror!void {
  const stdout = std.io.getStdOut().writer();
  const x:i32 = 1;
  var y:f32 = @as(f32, x);
  try stdout.print("{}\n", .{y}); // -> 1.0e+00
}

If you put the conversion in a function, it will not work:

fn conversion(i: i32) f32 {
  var k = @as(f32, i); // -> error: expected type 'f32', found 'i32'
  return k;
}
pub fn main() anyerror!void {
  const stdout = std.io.getStdOut().writer();
  const x:i32 = 1;
  var y:f32 = @as(f32, x);
  var z:f32 = conversion(x);
  try stdout.print("{}\n", .{y});
  try stdout.print("{}\n", .{z});
}

But if you use @comptime on function arguments, it will work:

fn conversion(comptime i: i32) f32 {
  var k = @as(f32, i); // -> no error
  return k;
}
pub fn main() anyerror!void {
  const stdout = std.io.getStdOut().writer();
  const x:i32 = 1;
  var y:f32 = @as(f32, x);
  var z:f32 = conversion(x);
  try stdout.print("{}\n", .{y}); // -> 1.0e+00
  try stdout.print("{}\n", .{z}); // -> 1.0e+00
}

If you do not want to use comptile, try @intToFloat() instead:

fn conversion(i: i32) f32 {
  var k = @intToFloat(f32, i);
  return k;
}
pub fn main() anyerror!void {
  const stdout = std.io.getStdOut().writer();
  const x:i32 = 1;
  var y:f32 = @as(f32, x);
  var z:f32 = conversion(x);
  try stdout.print("{}\n", .{y});
  try stdout.print("{}\n", .{z});
}

I cannot explain these results correctly. Please read the Zig documentation for clues.