In some source code I found this :
if etherbase != (common.Address{}) {
return etherbase, nil
}
etherbase is of type common.Address and it is defined as this:
// Lengths of hashes and addresses in bytes.
const (
HashLength = 32
AddressLength = 20
)
// Address represents the 20 byte address of an Ethereum account.
type Address [AddressLength]byte
The question is: what do parethesis mean in this context? Why can't they be omitted? Like this:
if etherbase != common.Address{} {
return etherbase, nil
}
The Go Programming Language Specification
A parsing ambiguity arises when a composite literal using the TypeName form of the LiteralType appears as an operand between the keyword and the opening brace of the block of an "if", "for", or "switch" statement, and the composite literal is not enclosed in parentheses, square brackets, or curly braces. In this rare case, the opening brace of the literal is erroneously parsed as the one introducing the block of statements. To resolve the ambiguity, the composite literal must appear within parentheses.
if x == (T{a,b,c}[i]) { … } if (x == T{a,b,c}[i]) { … }
An ambiguous composite literal common.Address{} before an if block { … }.
if etherbase != common.Address{} {
return etherbase, nil
}
An unambiguous composite literal (common.Address{}) before an if block { … }.
if etherbase != (common.Address{}) {
return etherbase, nil
}
For example,
package main
const AddressLength = 20
type Address [AddressLength]byte
func f(etherbase Address) (Address, error) {
// Unambiguous
if etherbase != (Address{}) {
return etherbase, nil
}
return Address{}, nil
}
func g(etherbase Address) (Address, error) {
// Ambiguous
if etherbase != Address{} {
return etherbase, nil
}
return Address{}, nil
}
func main() {}
Playground: https://play.golang.org/p/G5-40eONgmD