Foo() can have side-effects, taking a value from an array cannot, so Foo() is not necessarily dead code, whilst a[0] certainly is. _ serves multiple purposes,

Foo() can have side-effects, taking a value from an array cannot, so Foo() is not necessarily dead code, whilst a[0] certainly is. _ serves multiple purposes, not just for ignoring a return value. It's often used when you care about the side effect but not the return value, such as importation a driver for a database . You'll never use the library, so you import it as _ "db.driver.name/path/".