Golang空白变量类型声明[重复]

Question

This question already has an answer here:

• What does an underscore and interface name after keyword var mean? 2 answers
• Specs: What's the purpose of the blank identifier in variable assignment? [duplicate] 1 answer

What's the purpose of doing this:

var _ ipld.DAGService = (*ComboService)(nil)

Context:

type ComboService struct {
    Read  ipld.NodeGetter
    Write ipld.DAGService
}

var _ ipld.DAGService = (*ComboService)(nil)

// Add writes a new node using the Write DAGService.
func (cs *ComboService) Add(ctx context.Context, nd ipld.Node) error {
    return cs.Write.Add(ctx, nd)
}

Is it some kind of type assertion... interface implementation or?

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