Functional programming means, that your program is composed out of functions. A function only depends on its input parameters and the effect of applying a function is the returned function result. By this definition, functions don't have side effects.
Why do functions and functional programming matter?
- Functions are a very nice abstraction. Looking at the input and output values gives you the complete information about the data flow. This makes functions very easy to reason about.
- With the absence of side effects, you also have no unintended side effects, which plague all code which modifies state.
- Functions are easily testable, they do not depend on an environment but just the function parameters.
- For the same input a function necessarily always returns the same result, this also makes reasoning about a programs behavior easier.
- As a consequence that they only depend on their inputs, functions usually are very composeable.
While for certain tasks, modifying a global state can be the most efficient way of performing a computation, functional programming does not have to be slow, and in many cases the resulting program might even be faster. There are several reasons for this:
- With the lack of side-effects, functional programs can be relatively easy parallelized.
- With only local state involved, compilers can optimize the code inside functions more aggressively.
There are pure functional languages, but most modern languages allow you to write your program in a functional style. So it is possible to mix functional with object oriented programming.
Why do functions and functional programming matter?
- Functions are a very nice abstraction. Looking at the input and output values gives you the complete information about the data flow. This makes functions very easy to reason about.
- With the absence of side effects, you also have no unintended side effects, which plague all code which modifies state.
- Functions are easily testable, they do not depend on an environment but just the function parameters.
- For the same input a function necessarily always returns the same result, this also makes reasoning about a programs behavior easier.
- As a consequence that they only depend on their inputs, functions usually are very composeable.
While for certain tasks, modifying a global state can be the most efficient way of performing a computation, functional programming does not have to be slow, and in many cases the resulting program might even be faster. There are several reasons for this:
- With the lack of side-effects, functional programs can be relatively easy parallelized.
- With only local state involved, compilers can optimize the code inside functions more aggressively.
There are pure functional languages, but most modern languages allow you to write your program in a functional style. So it is possible to mix functional with object oriented programming.