Multiple nil types in Go. (opens in new tab)

(play.golang.org)

7 pointseonil12y ago7 comments

7 comments

6 comments · 2 top-level

_ak12y ago· 3 in thread

But: http://play.golang.org/p/J46-8OEWYS

`make` allocates and initializes `a`, setting it to nil effectively uninitializes the variable. See below, where I declare `c`, but don't initialize it. From the Golang spec, http://golang.org/ref/spec#Map_types, the value of an uninitialized map is nil.

http://play.golang.org/p/J46-8OEWYS

_ak12y ago

Don't tell me, I merely added one line of code to show that more information than the interface{} being nil is kept.

eonilOP12y ago

This is even more interesting.

LocalMan12y ago· 1 in thread

In Go, nil is a value, not a type. Assigning 'nil' to an interface only assigns the value, not the type. An interface has both a value and a type at runtime, but is "nil" only if both the value and the type are nil.

eonilOP12y ago

It's really hard to think the term nil is a value.

IMO, this is a bug in language design. If it's truly a value, I think they should choose a different term rather then `nil` as like they choose `panic/recover` instead of `throw/catch` because they're semantically different.

And also, I really don't know how should I detect nil reliably for an interface type.

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7 comments

6 comments · 2 top-level

_ak12y ago· 3 in thread

But: http://play.golang.org/p/J46-8OEWYS

cgearhart12y ago

`make` allocates and initializes `a`, setting it to nil effectively uninitializes the variable. See below, where I declare `c`, but don't initialize it. From the Golang spec, http://golang.org/ref/spec#Map_types, the value of an uninitialized map is nil.

http://play.golang.org/p/J46-8OEWYS

_ak12y ago

Don't tell me, I merely added one line of code to show that more information than the interface{} being nil is kept.

eonilOP12y ago

This is even more interesting.

LocalMan12y ago· 1 in thread

In Go, nil is a value, not a type. Assigning 'nil' to an interface only assigns the value, not the type. An interface has both a value and a type at runtime, but is "nil" only if both the value and the type are nil.

eonilOP12y ago

It's really hard to think the term nil is a value.

IMO, this is a bug in language design. If it's truly a value, I think they should choose a different term rather then `nil` as like they choose `panic/recover` instead of `throw/catch` because they're semantically different.

And also, I really don't know how should I detect nil reliably for an interface type.

j / k navigate · click thread line to collapse