Go Concepts - Functions
External
- Function type specification https://golang.org/ref/spec#Function_types
Internal
Function Definition
A function declaration starts with the func keyword and it consists in a series of statements applied on a number of inputs, resulting in a number of outputs. Same inputs will always result in the same outputs. Function do not depend on a type instance's state. From this perspective, functions are conceptually different from methods.
Syntax
func <name>( [parameter-identifier1] [type1], [parameter-identifier2] [type2], ...) [( <return-type1>, [return-type2], ...)] { // function's body statement1 statement2 ... return <return-value1>, <return-value2> }
The return type declarations are optional, if the function does not return anything.
A function may return one or more results.
Examples:
func add(a int, b int) (int) { return a + b; }
Function Literals
The main() Function
Built-in Functions
The built-in functions are available by default, without the need to import any package. They are what the specification calls pre-defined function identifiers. Their semantics depends on the arguments.
- Length and capacity len(), cap()
- close()
- Allocation: new()
- Making slices, maps and channels: make()
- Appending to and copying slices: append(), copy()
- Deletion of map elements delete()
- Handling panics panic, recover
- Manipulating complex numbers: complex, real, imag
- Bootstrapping print, println
go Built-In Function append
go Built-In Function copy
Closures
Anonymous function that capture local variables.
More about closures is available here.
Methods
A method defines the behavior of a type, and it relies on the state of an instance of the type. The method will - and it is supposed to - change the state. From this point of view, the method is conceptually different from a function.
A method is always exported by the package it is enclosed in.
Syntax
func <receiver> <method-name> (...) { // the rest of declaration is similar to a function's ... }