Go package import mode member visibility

Package import

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1） Absolute path import

gopath Management is just GOPATH/src Find packages in the directory

If it is gomod then The prefix is the current project module name , If it is an external package, it is the name of the entire module   

import（
  go  Standard package 
   Third party package 
   Local package 
）

2) Relative path import

gomod Method is no longer supported , Only in gopath Mode supports . Look in the directory where the current file is located , This is not recommended , Know that you can .

Example ：import "./gpkgname/pkg02"

3) Point import

When importing the members in the package at the call point, you can directly use the member name to call （ Omit package name , Generally, it is not used very much ）

If there are two bags , There's... In it Add Method , If you use point import , So use Add Which one to use in the end ？ There will be problems , So this method is also less used .

4) Alias import

When importing the same package name from different paths , You can import aliases to rename packages , To avoid conflict  

5) Underline import

Go Package import not allowed but not used , In some cases, you need to initialize the package , Import using whitespace as an alias , So that the initialization function in the package can execute .（ Sometimes you use the driver package , We need to initialize the contents of the package , Initialization package only , It doesn't call the functions or variables inside , At this time, you have to use underline to import .）

Member visibility

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Go Language uses the case of the initial letter of the name to judge the object ( Constant 、 Variable 、 function 、 type 、 Structure 、 Such method ) Access rights of , The initial capital letter indicates that it is visible outside the package ( Open ), Otherwise, it is only accessible in the package ( Inside ).

You can define some contents in the package that you don't want to be accessed from outside , Write a function for internal use , This involves the accessibility of the members in the package .

In bag Capital letters are visible outside the package , The lowercase initials can only be seen inside the package . It can be seen whether it is possible to call .

Function type visibility

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If the invisible member wants to be called , It can be used in visible members , This can be used by callers outside the package . 

Variable type accessibility

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  Changing this variable outside will also affect the variable inside the package , If it is lowercase, it cannot be accessed outside the package .