Demonstrative, selective slice-memory-minimizer for Go
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A trivial demonstration of (some of) Go's reflect capabilities.

This package provides a function, Slice, which takes an arbitrary slice type and returns a value of that same type (boxed in an interface{}) that may or may not have the property len(slice) == cap(slice), depending on the provided abs and rel parameters, which are an int and a float32, respectively.

abs is a threshold, as the integral capacity for extra elements past the length, that the output slice should not exceed. Ex: an abs of 5 means that cap - len should be less than or equal to 5.

rel is a threshold, as a ratio of 'extra' capacity, that the output slice should not exceed. Ex: 0.25 means that the capacity should be no more than 25% greater than the length.

If either of these thresholds is exceeded, the returned slice will point to a freshly allocated copy that has no extra capacity. As a special case, if the input slice is zero-length, a nil slice will always be returned. If neither threshold is exceeded, the original slice will be returned.

SlicePtr is a convenience function; unlike Slice, which, as with append, takes and returns a slice, this takes a pointer to a slice, which it modifies in place, saving the need for unboxing.

Usage notes

Should you use this? Probably not. While this does work, it is currently intended to serve as a Go reflection demonstration. In the cases where this behavior is useful (a very large slice of long-term data created via append), it is better to spend the one or two lines of code to do this using the builtin functions--you'll almost certainly know whether or not it's worth doing (application dependent), and the builtins will be much faster.