Free type variable

[lars-reimann]

Related to #1135

Is your feature request related to a problem?

The following code currently produces an error Expected type 'Map<String, Int>' but got 'Map<Nothing, Nothing>':

package test

@Pure fun f(a: Map<String, Int>)

pipeline myPipeline {
    f({});
}

The issue here is that the type parameter K of Map is invariant. We currently have no way to indicate that K is completely free in {}

Desired solution

Add a new type (free type/unbound type/star type) that can only be computed, but not written directly in programs. It should be compatible to any type.

Possible alternatives (optional)

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Additional Context (optional)

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