Go Go?

Go Lunch 'n Learn example code. Most of the code is taken from http://tour.golang.org.

Anything that is not covered in this lunch 'n learn can likely be found here: http://golang.org/doc/effective_go.html

Interesting Aspects

• Go is built has a concurrent, garbage-collected language with fast compilation. Large applications should compile in a few seconds on a single machine.
• When compiling, unused variables and imports are considered errors and stop compilation.
• Go does not have exceptions because the designers believe them to be cumbersome. Instead Go has Defer, Panic, and Recover.

Hello World

Packages

• All Go programs are made up of packages
• Programs start running in package main
• import is used to import other packages

Exported Names

• After importing you can refer to the name a package exports
• Go exports anything that begins with a capital letter

Variables

• Declare with either var or := (:= can only be used inside functions)
• Type is declared after variable name
• If initializer is present, type can be ommitted
• := uses implicity typing
• Constants can be a character, string, boolean, or a numeric value

Functions

• Return value type always comes after parameter list
• When consecutive parameters share a type it can be shortened
• Functions can return any number of results
• Go functions can return result parameters that act as normal variables while inside the function and return their current value on return

Loops and Conditions

If Statements

• No ( ) and { } are required
• Can start with short statement before the execution of condition
• Variables declared in the statement are only in scope until the end of the if block

For loop

• Go only has a for loop
• As with C, the pre and post statements can be empty and then no ; are required
• For an infinite loop the keyword for can just be used

Switch Statements

• Evaluates from top to bottom
• Automatically breaks unless a case ends with a fallthrough statement
• Switch statement without condition can be used for long if-then-else chains

Data Structures

Pointers

• No pointer arithmetic

Structs

• A collection of fields
• Uses the dot accessor
• new(T) function allocates a zeroed struct and returns a pointer to it

Slices

• Points to an array of values
• len(s) is used to get the length of a slice
• Can be re-sliced, creating a new slice value that points to the same array
  • expression: s[lo:lo]
  • evaluates from lo through hi-1, inclusive
  • s[lo:lo] is empty and s[lo:lo+1] has one element
• Slices are created with the make() function
• cap(s) is used to get the capacity of a slice

Maps

• Key value pair structure
• Can be created with make()
• delete() is used to remove an object from a map
• A loopup returns two parameters, the value (if any) and a boolean indicating if the element exists in the map

Closures

• Work just like closures in JavaScript

Methods and Interfaces

Methods

• Go does not have classes
• Methods can be attached to structs
• The method receiver appears between func and the method name
• The method receiver should be a pointer to the type, this allows the method to modify properties of the type

Interfaces

• Interface type is defined as a set of methods
• A value of interface type can hold any value that implements those methods
• Allows for increased decoupling

Concurrent Programming

Goroutines

• Lightweight thread, managed by Go runtime
• go is the keyword used to start a new goroutine

Channels

• Typed conduit through which you can send and receive values with the channel operator, <-
• Must be created before use
• By default, sends and receives block until the other side is ready. This allows goroutines to synchronize without explicit locks or condition variables
• Can be buffered, provide buffer amount as the second argument to make
• Sends to a buffered channel block only when the buffer is full. Receives block when the buffer is empty.

Range and Close

• A sender can close a channel to indicate that no more values with be sent
• A receiver can check if a channel is open by utilizing the second return value
• A range loop can be used to receive values until the channel is closed

Select blocks

• A select block blocks until one of its cases can run, then it executes that case. It chooses one at random if multiple are ready.
• default can be used to create a non-blocking pattern