examples

Go examples ⬆

Directory examples\ contains Go code examples coming from various websites - mostly from the Go project.

basics Example

This example has the following directory structure :

> tree /a /f . | findstr /v /b [A-Z]
|   build.bat
|   go.mod
|   magefile.go
\---src
    \---main
            basics.go

Command build.bat executes the Go command %GOROOT%\bin\go build with the appropriate parameters and runs the generated executable basics.exe ¹:

> build -verbose run
Compile 1 Go source file to directory "target"
Execute target "target\basics.exe"
My favorite number is 2
3.141592653589793
55
world hello
7 10
2 true false no!
Type: bool Value: false
Type: uint64 Value: 18446744073709551615
Type: complex128 Value: (2+3i)
Type: int32 Value: 8658
Hello 世界
Happy 3.14 Day
Go rules? true

hello Example ▴

This example has the following directory structure :

> tree /a /f . | findstr /v /b [A-Z]
|   build.bat
|   go.mod
|   magefile.go
|   Makefile
\---src
    +---main
    |       hello.go
    \---test
            hello_test.go

Command build.bat executes the Go command %GOROOT%\bin\go build with the appropriate parameters and runs the generated executable hello.exe :

> build -verbose run
Compile 1 Go source files to directory "target"
Execute target "target\hello.exe"
hello, world

Build tool mage.exe takes its Makefile-like runnable targets from the Go file mage.go; for instance targets clean and build :

Note : Mage supports a makefile-style tree of dependencies using the helper library github.com/magefile/mage/mg. To declare dependencies, pass any number of dependent functions to mg.Deps.

> mage clean build & target\hello.exe
hello, world

Adding the Mage option -v will print some progress messages :

> mage -v clean build & target\hello.exe
Running target: Clean
Running target: Build
hello, world

Finally, one may also invoke the Mage target run directly (target run requires at least one argument, thus the dummy argument 0 below):

> mage clean run 0
hello, world

WIP

Footnotes ▴

[1] Code disassembling ↩

The Go command objdump prints out the disassembled binary code for the generated executable, e.g. target\basics.exe; here is an excerpt of the main function (source: basics.go):

> go tool objdump -S target\basics.exe | awk 'BEGIN{n=0}/basics/{n=1}{if (n^>0) print $0}'
TEXT main.main(SB) K:/examples/basics/src/main/basics.go
func main() {
  0x49a800              4c8da42490feffff        LEAQ 0xfffffe90(SP), R12
  0x49a808              4d3b6610                CMPQ R12, 0x10(R14)
  0x49a80c              0f862d060000            JBE 0x49ae3f
  0x49a812              55                      PUSHQ BP
  0x49a813              4889e5                  MOVQ SP, BP
  0x49a816              4881ece8010000          SUBQ $0x1e8, SP
    fmt.Println("My favorite number is", rand.Intn(10))
  [...]
    fmt.Println("Go rules?", Truth)
  0x49adc5              440f11bc2498000000      MOVUPS X15, 0x98(SP)
  0x49adce              440f11bc24a8000000      MOVUPS X15, 0xa8(SP)
  0x49add7              488d0da2950000          LEAQ type:*+37760(SB), CX
  0x49adde              48898c2498000000        MOVQ CX, 0x98(SP)
  0x49ade6              488d0dd3890400          LEAQ runtime.buildVersion.str+96(SB), CX
  0x49aded              48898c24a0000000        MOVQ CX, 0xa0(SP)
  0x49adf5              488d0d84990000          LEAQ type:*+38784(SB), CX
  0x49adfc              48898c24a8000000        MOVQ CX, 0xa8(SP)
  0x49ae04              488d0d7d370c00          LEAQ runtime.staticuint64s+8(SB), CX
  0x49ae0b              48898c24b0000000        MOVQ CX, 0xb0(SP)
       return Fprintln(os.Stdout, a...)
  0x49ae13              488b1d76f70c00          MOVQ os.Stdout(SB), BX
  0x49ae1a              488d05778f0400          LEAQ go:itab.*os.File,io.Writer(SB), AX
  0x49ae21              488d8c2498000000        LEAQ 0x98(SP), CX
  0x49ae29              bf02000000              MOVL $0x2, DI
  0x49ae2e              4889fe                  MOVQ DI, SI
  0x49ae31              e80a83ffff              CALL fmt.Fprintln(SB)
}
  0x49ae36              4881c4e8010000          ADDQ $0x1e8, SP
  0x49ae3d              5d                      POPQ BP
  0x49ae3e              c3                      RET
func main() {
  0x49ae3f              90                      NOPL
  0x49ae40              e8fbeffcff              CALL runtime.morestack_noctxt.abi0(SB)
  0x49ae45              e9b6f9ffff              JMP main.main(SB)

lensm – a Go assembly and source viewer – is a nice alternative to view both assembly and source (see post "Easy to read Golang assembly output?" on stackoverflow)

> go install loov.dev/lensm@main
go: downloading loov.dev/lensm v0.0.4
go: downloading gioui.org v0.3.1
go: downloading golang.org/x/exp/shiny v0.0.0-20230713183714-613f0c0eb8a1
go: downloading github.com/go-text/typesetting v0.0.0-20230803102845-24e03d8b5372
go: downloading golang.org/x/exp v0.0.0-20230713183714-613f0c0eb8a1
go: downloading golang.org/x/image v0.5.0
go: downloading golang.org/x/text v0.7.0
go: downloading github.com/tetratelabs/wabin v0.0.0-20230304001439-f6f874872834
go: downloading golang.org/x/sys v0.1.0
go: downloading gioui.org/cpu v0.0.0-20210817075930-8d6a761490d2
go: downloading gioui.org/shader v1.0.8
go: downloading golang.org/x/arch v0.2.0
 
> where lensm
%USERPROFILE%\go\bin\lensm.exe

The following screenshot presents the same assembly code as above :

> lensm -filter "main" target\basics.exe

---

mics/February 2025 ▲