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Append

The built-in append function is used to dynamically add elements to a slice:

func append(slice []Type, elems ...Type) []Type

If the underlying array is not large enough, append() will create a new underlying array and point the returned slice to it.

Notice that append() is variadic, the following are all valid:

slice = append(slice, oneThing)
slice = append(slice, firstThing, secondThing)
slice = append(slice, anotherSlice...)

Assignment

We've been asked to add a feature that extracts costs for a given day.

Complete the getDayCosts() function. It accepts a slice of cost structs and a day int, and it returns a float64 slice containing that day's costs.

Create an empty, non-nil float64 slice.
Use append() to add each matching cost's value to the slice.
Return the slice.