shift operator where first operand is an untyped bigint always results in a bigint

[thehowl]

package main

func main() {
        x := 11
        y := uint64(1 << x)
        println(y)
}

// panic running expression main(): cannot convert BigintKind to Uint64Kind 

The solution is to explicitly convert the first operand to a uint64...

package main

func main() {
	x := 11
	y := uint64(uint64(1) << x)
	println(y)
}

// 2048

[deelawn]

I'm not sure but on the surface the solution to this may be related to the solution in #1423

[ltzmaxwell]

Hi,
I've submitted a fix at #1426. It's about the type check/conversion for some special case, e.g. shift expr or any expr involve a shift expr.

[thehowl]

Let me add an issue related to this. I'll avoid making this a separate issue, mostly because I believe Maxwell's #1426 likely tackles this as well, but I want to publicly document another situation where this creates issues.

Consider the following code:

package main

func main() {
	x := 1024
	p := 10
	if x != 1<<p {
		println("WHAT?")
	}
}

This will print WHAT?, unexpectedly (Go prints nothing).

Because x and 1 << p are different types (per the issue title, 1 << p is a Bigint), they are considered different.

Naturally, changing 1 to int(1) makes the code work as it should. ;_;

@ltzmaxwell, rest assured I will try to review your PR as soon as possible because tracing down bugs like these destroys my mental sanity.

[ltzmaxwell]

Hi Morgan @thehowl,
this works:

package main

func main() {
	x := 1024
	p := 10
	if x != 1<<p {
		println("WHAT?")
	} else {
		println("nothing")
	}
}

// Output:
// nothing

[thehowl]

@ltzmaxwell I'm getting WHAT? on master :)

Or do you mean on your branch?

[ltzmaxwell]

@ltzmaxwell I'm getting WHAT? on master :)

Or do you mean on your branch?

Oh yes, I mean on my branch. Sorry for the ambiguity.