CommandLine

• After parsing flags you can get other arguments via: flag.Args() (array) or flag.Arg(i) specific arg. flag.Narg = number of args

Time

• Layout string in time.Parse and time.Format expects this date (reference date): 01/02/2006  Jan 2 15:04:05 2006 MST (Note the date should be this specific date and time for it to parse successfully). Following shows some example:

time.Parse("01/02/2006", "10/02/2024")
time.Parse("02 of 01 2006", "02 of 10 2024")

Sql

• For database sql, checkout this wiki

Logging

• For serial logging, checkout slog

Golang build

• To cross compile go binary for different os and arch run:

env GOOS=target-OS GOARCH=target-architecture go build package-import-path

where target-os can be: linux, darwin, android, windows, freebsd, netbsd, openbsd, dragonfly, plan9
where target-architecture can be: arm, arm64, amd64

• Use embed package to add files to binary at compile time

Local dependency

To use local version of the dependency, you can clone the deps in dir $DEP, then use replace directive in go mod

$ go mod edit -replace github.com/google/go-cmp=$DEP

Array, Slices

• Array is the building block of contingous items, contains size as part of it's definition. eg var buffer [256]byte. Arrays are always fixed size.
• Slice is a datastructure which describes a contiguous section of array: var slice []byte = buffer[100:150]. Behind the scenes, it contains the pointer to array, length and capacity (maximum length to which slice can extend).

String, Rune, Character, Byte

• String in golang is slice of bytes
• String literals are always utf-8 encoded. (Go source code) eg const nihongo = "日本語"
• In unicode standard, each character is represented by "code point" eg, U+2318 represents ⌘ , in golang this code point is referred as rune (aliased to int32)
• When you range through a loop, it decodes 1 utf-8 length rune on each loop

Import local modules

Import other packages rather than main package

import (
  "noc-manager/pkg/models"
)

Run go mod edit -replace noc-manager=../../noc-manager to add a local dependency & run go mod tidy

Tip: Name modules as simple names rather than git urls unless you're planning on publishing them. Otherwise you might get weird issues.

JSON or YAML omitempty or ignore

type T struct {
    F int `yaml:"a,omitempty"`
    B int `yaml:"-"` // this field will be ignored from rendering
}

type T struct {
    F int `json:"a,omitempty"`
    B int `json:"-"` // this field will be ignored from rendering
}