delete map key in go

Question

I have a map   var sessions    map string  chan int     How do I delete sessions key    I tried   sessions key    nil false    That didn t work      Update  November 2011    The special syntax for deleting map entries is removed in Go version 1      Go 1 will remove the special map assignment and introduce a new built-in function  delete  delete m  x  will delete the map entry retrieved by the expression m x

User · Answer

From Effective Go   To delete a map entry  use the delete built-in function  whose arguments are the map and the key to be deleted  It s safe to do this even if the key is already absent from the map  delete timeZone   quot PDT quot       Now on Standard Time

User · Answer

Copied from Go 1 release notes  In the old language  to delete the entry with key k from the map represented by m  one wrote the statement   m k    value  false   This syntax was a peculiar special case  the only two-to-one assignment  It required passing a value  usually ignored  that is evaluated but discarded  plus a boolean that was nearly always the constant false  It did the job but was odd and a point of contention   In Go 1  that syntax has gone  instead there is a new built-in function  delete  The call  delete m  k    will delete the map entry retrieved by the expression m k   There is no return value  Deleting a non-existent entry is a no-op   Updating  Running go fix will convert expressions of the form m k    value  false into delete m  k  when it is clear that the ignored value can be safely discarded from the program and false refers to the predefined boolean constant  The fix tool will flag other uses of the syntax for inspection by the programmer

User · Answer

Strangely enough   package main  func main          var sessions   map string  chan int        delete sessions   moo        seems to work  This seems a poor use of resources though   Another way is to check for existence and use the value itself   package main  func main          var sessions   map string  chan int        sessions  moo     make  chan int          ok    sessions  moo        if ok           delete sessions   moo

User · Answer

delete sessions   anykey     These days  nothing will crash

User · Answer

Use make  chan int  instead of nil  The first value has to be the same type that your map holds   package main  import  fmt   func main          var sessions   map string  chan int       sessions  somekey     make chan int       fmt Printf    d n   len sessions      1         Remove somekey s value from sessions     delete sessions   somekey        fmt Printf    d n   len sessions      0     UPDATE  Corrected my answer

[map] delete map[key] in go?

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