Go init initialization function

main Bag and init  function

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main A package is used to declare that it tells the compiler to compile the package into a binary executable , stay main In bag main Function is the entry of a program , No return value , No parameter .

main Functions are often written in main Inside the package , Not elsewhere .

init function

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init Function is used to initialize the package , No return value , No parameter . It is recommended that only one... Be defined for each package .init Function in import

Package is called automatically （const->var->init）.

The initialization function is executed when the package is imported

 

_ Used for initialization import  

You can see main There's nothing in it , But it printed init The statement in the function .

Load when the program is executing main package ,main And then load other , stay main It loads programs from top to bottom , Load the program first , When loading the program, I found import 了 , This is the time to find import Package and load .

When the package is found for loading, it will be loaded from top to bottom , If there is import Then you will load other . Because there are many under a bag go file , So these files will be loaded when loading . After loading, you will see what is available init function , Then carry out all the init function , Execute all init So the first one import The import is complete .

import After that, it will be executed main Function loading , If main There are also init Function, then execute it first init Function initialization , It will not be executed until the execution is completed main function .（ A package can contain multiple init function ）

If there are more than one under a package go file , There's... In it init This function , So the order of execution is random .

init It can be used later when it is related to the database , Initialize the connection , This is also the principle of initializing some drivers .

There are many more packages that use underscores _ To import , In fact, it is to execute the init function .