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dictionarygocomposite-literals

Extend map from other packages at compile time

I'm trying to extend a map across packages at 'compile time'. Is this possible?

I have package A with a predefined map:

package A

var MyMap = map[string]string{"key1": "value", "key2": "value"}

And I would like to extend the map during 'compile time'. This shall be done in another package. E.g. like so (not working code ofc.):

package B

import "A"

A.MyMap.Slice1["key3"] = "value" // extend the map during compile time

Is this somehow possible?

Solution

  • You can't do this "at compile" time. In fact, the composite literal that package A uses, that also will be constructed and used at runtime. There are no composite literal constants.

    Going further, whatever code you write in package B, if it imports package A, code of package B will only run after package A has been initialized, including the map you posted.

    If you want A.MyMap to have a different value before it can be seen by any other package, you should modify the source of package A. This could be a generated additional file, which could use a package init() function, assigning a new value to MyMap, or adding new values to it.

    If you can, you could also modify package A so that the initialization of MyMap is moved to a different source file, one that can be generated.