Unity's #pragma strict, #pragma downcast and other command sharing

At the beginning of some unity scripts you can often see #pragma strict, #pragma downcast, #pragma implicit instructions, and some unity scripts do not have these instructions, what is the purpose of these instructions?
#pragma strict, the meaning of this directive is forced input, that is, when declaring a variable, we need to declare exactly what type of variable it is, rather than let the compiler infer the type of the variable by itself, so it is not possible to use a random name and have the compiler instantiate it for you. For example, after using this directive, we arbitrarily declare a variable:

Private Var bobby;//is not possible,

and need this:

Private Var bobby:gameobject;//this can be

By using #pragma strict, you can force us to develop good programming habits, but this is not something that must be done in unity.

and #pragma downcast and #pragma implicit command, it can be used with #pragma strict directive, so as to achieve "strict in the loose", it is a bit of meaning. First look at the #pragma implicit directive, which means that in the use of #pragma strict instructions, with this directive and can implicitly declare variables,

For example:

   #pragma strict    foo = 5;//Can not    #pragma strict    var foo = 5;//can     #pragma strict     #pragma implicit     fo o = 5; This sentence is possible by using the #pragma implicit.

The #pragma downcast statement allows the variable to be used from super (parent type) to the #pragma strict instruction.

Sub (sub) type conversions, for example:

    #pragma strict     var go:gameobject;    var clone:gameobject = instantiate (go); This statement is not possible because the object type returned after instantiate//Is object, not gameobject     #pragma strict     #pragma downcast     var go: Gameobject;    var clone:gameobject = instantiate (go); This statement is possible, using #pragma downcast     //The following statement is also possible:  #pragma strict  var go:gameobject;  var clone:gameobject = Instantiate (go) as gameobject; This statement is also possible because the//type is converted as.

Unity's #pragma strict, #pragma downcast and other command sharing