changetype number to bool

[LiaoPeng]

The assemblyscript code

assert(true == changetype<boolean>(1));
assert(false == changetype<boolean>(0));
assert(true == changetype<boolean>(3));
assert(false == changetype<boolean>(2));

I expected:
assert(false == changetype(2)); // failed

In fact, all asserts passed.

It seemed that changetype number to bool just get the last bit.

[dcodeIO]

Note that changetype isn't meant for casting, but actually for changing between a reference and a value type, i.e. between SomeObject and usize. This is unsafe and shouldn't be used unless absolutely necessary.

For casting, there is <bool>2, or its portable version bool(2). Also, conversion to bool is performed through & 1 currently, which might be unexpected and might need to be changed to != 0 maybe. In general, I'd recommend to do 2 != 0 for clarity instead of casting.

[MaxGraey]

I think change this to != 0 instead & 1 is right approach

[dcodeIO]

Does C/C++ handle bool specifically as != 0?

[MaxGraey]

Currently assert(true == <bool>(2)); is fail btw. Rust and C++ use != 0 approach.

0b10 & 1 = 0 // false

[dcodeIO]

Ok, so we should add a special case for bool I guess.

[dcodeIO]

For reference:

#include <stdbool.h>

#define WASM_EXPORT __attribute__((visibility("default")))

WASM_EXPORT
bool test(int i) {
  return ((bool)i) == true;
}

compiles to

  (func $test (export "test") (type $t1) (param $p0 i32) (result i32)
    get_local $p0
    i32.const 0
    i32.ne
  )

so != 0 seems good.

[dcodeIO]

Fixed in #343 for casts. Please keep in mind that changetype isn't meant for this.

[LiaoPeng]

cool