Captured value in inline else is different from actual value

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1

For context, Value struct is defined as follow

pub const Value = union(Type) {
    Bool: bool,
    Nil: void,
    Number: f64,
    Obj: *Obj,

    pub fn eql(self: Value, other: Value) bool {
        switch (self) {
            .Obj => |obj| {
                if (!other.isObj(obj.type)) return false;
                switch (obj.type) {
                    inline else => |t| {
                        const obj_a = self.asObj(t).?;
                        const obj_b = self.asObj(t).?;
                        return obj_a.eql(obj_b);
                    },
                }
            },
            inline else => |value, tag| {
                return tag == std.meta.activeTag(other) and value == @field(other, @tagName(tag));
            },
        }
    }
}

The function in question is a method that compares two Values.
Here’s the screenshot of the function and the debugging state:

image
image1920×1626 143 KB

As you can see in the debugger, the actual value of obj.type is String, but the captured value t comes back as Closure. It’s not obvious to me why this happens, so I would appreciate some help. I’m not sure what else to provide as context so please feel free to ask.

2

The debugger state is wrong. The bug came from my code, the fix is

- const obj_b = self.asObj(t).?;
+ const obj_b = other.asObj(t).?;
3

It seems most people are using the Crafting Interpreters book to learn Zig. I’m one of those, too, only a few pages in front of you. Welcome!

3 Likes
4

I don’t know about most, but a quick search here seems to show that it’s a common path! I’ve seen a few people say that they do Go for the first half and Zig for the second, which is what I did!