What's the use of var _ Querier = (*Queries)(nil)

[FotiadisM]

I don't understand what this line does or why is it useful. Could some pleas explain it me? Thank you very much

type Querier interface {
    // ...
}

var _ Querier = (*Queries)(nil)

[go-aegian]

var _ Querier = (*Querier)(nil)

allows compiler to verify a struct implements the interface