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Go's simplicity is merely syntactical. The semantics can be subtle and not entirely aligned with intuition honed after x years of working with C-like language X

Go's simplicity is merely syntactical. The semantics can be subtle and not entirely aligned with intuition honed after x years of working with C-like language X. This is an observation and not a critique. > I learned yesterday that `x == nil` can return false even if x is nil so long as ... In other words: http://play.golang.org/p/YV5ylbQN4j http://play.golang.org/p/YV5ylbQN4j Thanks for the heads-up! That was news to me.

tptacek 11y ago
When does it make sense to compare a string with nil?
- eternalban 11y ago
  It doesn't but the function admits a T. It actually makes perfect sense, it is just a bit subtle.
oconnor663 11y ago
In the playground you have there, the string `v` is implicitly initialized to the empty string, which is not equal to nil. I'm referring to a different condition, where two different values are explicitly set to nil. Check this out: https://play.golang.org/p/qMmg7yOAKO https://play.golang.org/p/qMmg7yOAKO
- infogulch 11y ago
  Yes this is what trips many people up. One reason `(* T)(nil) != nil` is because a `(* T)(nil)` can still have pointer methods called on it, and it can still work fine (as long as the receiver is never dereferenced, of course): https://play.golang.org/p/rup5cqapEU https://play.golang.org/p/rup5cqapEU
falcolas 11y ago
Actually, the issue mentioned by the OP is covered here: http://golang.org/doc/faq#nil_error http://golang.org/doc/faq#nil_error Basically, if you pass 'nil' of one type into an argument which accepts an interface of another type, the nil is no longer nil, but an interface wrapper around a nil (which is not nil). So: var buf *bufio.Reader // a nil value if this is passed into a function with a signature of func foo(buf io.Reader) then when in function foo: foo(buf) // valid, and buf is nil here //inside foo: if buf != nil { // but buf is not nil here, so this is true buf.Read() // Panics because nil has no function Read.
- pcwalton 11y ago
  The post you were replying to was talking about whether the behavior is intuitive, not whether it is documented.
- Redoubts 11y ago
  I'm confused, how is that different from https://play.golang.org/p/rup5cqapEU https://play.golang.org/p/rup5cqapEU where calling on the nil value of T seems to work.

tptacek 11y ago

When does it make sense to compare a string with nil?

eternalban 11y ago
It doesn't but the function admits a T. It actually makes perfect sense, it is just a bit subtle.

oconnor663 11y ago

In the playground you have there, the string `v` is implicitly initialized to the empty string, which is not equal to nil. I'm referring to a different condition, where two different values are explicitly set to nil. Check this out: https://play.golang.org/p/qMmg7yOAKO https://play.golang.org/p/qMmg7yOAKO

infogulch 11y ago
Yes this is what trips many people up. One reason `(* T)(nil) != nil` is because a `(* T)(nil)` can still have pointer methods called on it, and it can still work fine (as long as the receiver is never dereferenced, of course): https://play.golang.org/p/rup5cqapEU https://play.golang.org/p/rup5cqapEU

falcolas 11y ago

Actually, the issue mentioned by the OP is covered here: http://golang.org/doc/faq#nil_error http://golang.org/doc/faq#nil_error Basically, if you pass 'nil' of one type into an argument which accepts an interface of another type, the nil is no longer nil, but an interface wrapper around a nil (which is not nil). So: var buf *bufio.Reader // a nil value if this is passed into a function with a signature of func foo(buf io.Reader) then when in function foo: foo(buf) // valid, and buf is nil here //inside foo: if buf != nil { // but buf is not nil here, so this is true buf.Read() // Panics because nil has no function Read.

pcwalton 11y ago
The post you were replying to was talking about whether the behavior is intuitive, not whether it is documented.
Redoubts 11y ago
I'm confused, how is that different from https://play.golang.org/p/rup5cqapEU https://play.golang.org/p/rup5cqapEU where calling on the nil value of T seems to work.