Go: Beyond the BasicsJoey Gibson

Senior ArchitectLancope, Inc.

@joeygibson

Wednesday, July 31, 13

Agenda• $GOPATH

• Project Organization

• Packages

• Structs

• Methods

• Interfaces

• Regular Expressions

• Functions are First-Class Citizens

• Goroutines and Channels

Wednesday, July 31, 13

$GOPATH

• A series of directories where Go looks for sources and libraries

• export GOPATH=~/Projects/gobtb:~/Projects/gotest

• Must contain a src/ directory, with package directories under that

• Will contain pkg/ directory after doing an install

• go  env -- shows all variables

Wednesday, July 31, 13

Bash

export GOROOT=/Users/<yourname>/Projects/go

export GOPATH=/opt/go-3rdparty:/Users/<yourname>/Projects/gotest

export PATH=$GOROOT/bin:$PATH:${GOPATH//://bin:}/bin

Wednesday, July 31, 13

Project Organization

• Project directory should have a src/ subdirectory

• Files in subdirectories of src/ that are in a package (!main) install to pkg/$GOOS_$GOARCH

• (e.g. src/foo for a “foo” package)

• go  install  foo will install foo.a in pkg/$GOOS_$GOARCH

• Files in subdirectories of src/ that are in package main, install to the bin/ directory (e.g. src/bar for a bar command)

• go  install  bar will install bar executable in bin/

Wednesday, July 31, 13

Packages• Should live in src/foo, src/bar, etc.

• Everything in the directory will get built into a single “thing” (i.e. foo.a, bar[.exe])

• Can reference each other; don’t use relative references (e.g. import  “../bar”)

• Can have subpackages

• package quux -- in src/foo/quux/*.go

• imported as “foo/quux”

• referenced as quux.Q()

• Don’t forget aliases -- import xxx foo/quux

Wednesday, July 31, 13

Structs

• Similar to C structs; data only

• Can have methods associated with them

• Can be created on stack or heap; compiler decides which based on context

• Can be nested

• ... also anonymously...

Wednesday, July 31, 13

Methods

• Look like functions, but have an extra type clause that specifies which “thing” the method is for

• The type clause can take a thing, or a pointer to a thing

• If specified as *thing, no need to provide address; Go will handle it

Wednesday, July 31, 13

Interfaces• Specify required methods a type must provide

• Any named type can implement methods to implement an interface

• No need to declare that a thing implements an interface

• A thing can implement multiple interfaces

• Like duck typing in Ruby, Python, etc., but...

• A compile-time error will occur if trying to pass a thing that doesn’t implement a required interface

• Convention is to name with -er suffix: Printer, Looper, Planner, etc.

Wednesday, July 31, 13

Interfaces: Semi-Generic

• Declaring that a function takes interface{} will allow the function to accept anything as a paramerter

• But that means anything at all

Wednesday, July 31, 13

Regular Expressions

• Full support for Perl regex

• Provides compilation, matching, finding, splitting, and replacing

• Go’s backquotes allow for things like `H\wllo` without doubling backslashes

Wednesday, July 31, 13

First-class functions

• Can be

• assigned to variables

• passed as parameters to other functions

• stored in maps, arrays, etc.

• created/executed anonymously

Wednesday, July 31, 13

goroutines

• goroutines execute concurrently, on one or more threads according to availability

• Very lightweight; start with a 4k stack

• Stack grows and shrinks as necessary

• Run in same address space as calling process...

• Are not parallel by default!

• To parallelize: set GOMAXPROCS > 1

Wednesday, July 31, 13

goroutine rule

• “Do not communicate by sharing memory; instead, share memory by communicating.”

Wednesday, July 31, 13

Channels• Datatype providing communication and

synchronization between goroutines

• Channels have a type; only one type of thing can be pushed over a channel

• Created using make()

• Can be buffered or not (defaults to unbuffered)

• Can be declared read-only or write-only...

• Unbuffered means sends and receives block until both sides are ready

Wednesday, July 31, 13

Channels

• The <-­‐ operator pushes to, or pulls from, a channel

• The range operator reads from a channel, until it’s closed

• Close with close()

Wednesday, July 31, 13

Resources

• Testify: https://github.com/stretchr/testify

• Goclipse: https://code.google.com/p/goclipse/

Wednesday, July 31, 13