15.10 Higher-order Functions
On the surface, lambdas and function references do not seem to be particularly compelling features. The possibilities that these features offer become more apparent, however, when we consider that lambdas and function references have the same capabilities of many other data types. In particular, these may be passed through as arguments to another function, or even returned as a result from a function.
A function that is capable of receiving a function or lambda as an argument, or returning one as a result is referred to as a higher-order function.
Before we look at what is, essentially, the ability to plug one function into another, it is first necessary to explore the concept of function types. The type of a function is dictated by a combination of the parameters it accepts and the type of result it returns. A function which accepts an Int and a Double as parameters and returns a String result for example is considered to have the following function...
