Function Pointer Usage

Problems

Have to create the function and name it
Naming things is good when we have a good name but a nuisance when we don't
Functions often cannot be defined close to where they are used, so we have to search for it

Solution: Lambda Function

Also known as an anonymous function
Originated from Church's lambda calculus (λ-calculus)
C++11 feature
The simple form of a lambda function can be passed to a function pointer parameter
Lambda Function Syntax

Lambda Parts

Code	Term	Description
	Lambda
	Capture	Access to state from where the lambda is defined. We will leave it empty for now as this is a whole topic, and only an empty capture can be used with function pointer parameters.
	Parameters	Pass state from the code that calls the lambda function
	Return type	Can be any function return type. Optional if `void`. In many cases, the compiler can derive the return type.
	Body	Definition of the lambda function. Where the statements go. Anything you can do in a free function you can do in a lambda function

Empty Lambda

Only isolated usage because there is no state for the function to work on
Can be used for tracing or debugging

Lambda Parameter

Useful because the current state of the caller is passed to the callback
I.e., can compute based on the parameter

Lambda Parameters

lambda	Description
	IN parameter
	IN/OUT parameter

Lambda: `bool` comparision

Lambda: `int` comparision

Call qsort() with lambda function

Call std::sort() with lambda function

Comparison

Aspect	Function Pointer	Lambda Function
Definition	The function must be defined before it can be passed to a pointer	Defined inline where it's used, with its body enclosed in `{}` and parameters in `()`
Scope	Global or namespace scope for the function being pointed to	Scope is limited to where the lambda is defined
Capturing External Variables	Not directly possible. External variables must be passed as parameters	Can capture external variables from the surrounding scope either by value or by reference `[&]`
Portability	Highly portable and compatible with C interfaces	C++11
Performance	Slightly slower than a direct call	Provides more potential for compiler optimization

Issues

The capture ([]) and captured variables are very important
Inline lambda functions create several formatting issues