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Implement the missing type equality constraint specified in RFC 135.

Examples

fn sum<I: Iterator>(_: I) -> i32
where
    I::Item == i32 // or `I::Item = i32`
{
    // ...    
}

Note

As a matter of fact, $type = $type and $type == $type are syntactically valid and don't raise any feature gate warning/error if cfg'ed out! This is likely unintentional and should be ironed out.