update README.md

README.md

@@ -1,9 +1,15 @@
 # CAST IN THE NAME OF PHP, YE NOT GUILTY
+![Minimum PHP version: 7.0.0](https://img.shields.io/badge/php-7.0.0%2B-blue.svg)
+[![Packagist](https://img.shields.io/packagist/v/sj-i/php-cast.svg)](https://packagist.org/packages/sj-i/php-cast)
+[![Github Actions](https://github.com/sj-i/php-cast/workflows/build/badge.svg)](https://github.com/sj-i/php-cast/actions)
+[![Coverage Status](https://coveralls.io/repos/github/sj-i/php-cast/badge.svg?branch=master)](https://coveralls.io/github/sj-i/php-cast?branch=master)
+[![Psalm coverage](https://shepherd.dev/github/sj-i/php-cast/coverage.svg?)](https://shepherd.dev/github/sj-i/php-cast)
+
 ## ABOUT
-- you can cast any values in the weak mode manner, even if you are in the strict mode (strict_types=1)
+- You can cast any values in the weak mode manner, even if you are in the strict mode (strict_types=1).
 
 ## INSTALL
-```
+```bash
 composer require sj-i/php-cast
 ```
 
@@ -12,7 +18,7 @@ composer require sj-i/php-cast
 
 ## USAGE
 
-```
+```php
 use PhpCast\Cast;
 use PhpCast\NullableCast;
 
@@ -41,10 +47,31 @@ $float_value = NullableCast::toFloat(1);
 $bool_value = NullableCast::toBool(1);
 
 // TypeError
-$null_value = NullableCast:toInt('');
+$null_value = NullableCast::toInt('');
 // null
-$null_value = NullableCast:toInt(null);
+$null_value = NullableCast::toInt(null);
 ```
 
+## HOW IT WORKS
+- Return type declarations in weak mode files do the job.
+- `PhpCast\Cast` and `PhpCast\NullableCast` are defined in files declared as `strict_types=0`
+    - Though `strict_types=0` is the current default of PHP, it is explicitly declared to assert the intent.
+- The type checks for parameters are done in the caller mode, but the type checks for return values are always done in the callee mode.
+
+## "WHY WEAK MODE? I WANT TO USE STRICT MODE IN EVERYWHERE!"
+- To use `strict_types=1` without any `strict_types=0` codes, explicit casts have to be used for untyped data from external sources like DB or HTTP requests.
+- But in PHP, explicit cast like `(int)$foo` never fails with a few exceptions.
+    - `(int)'abc'` silently results to `0` and doesn't emit a warning.
+- So some validations are necessary before just using casts.
+- If explicit casts are used without proper validations by a lazy programmer, the purpose of the type declarations are totally ruined.
+    - This was, if I understand it correctly, one of the reasons that strict type checks weren't totally welcomed with open arms during the discussion introducing the scalar type hinting to PHP.
+- Defining proper rules of validations and type conversions is sometimes overkill.
+    - Even though defining them are always "correct" things to do, in humans life, there are times you don't need to be so correct.
+- Let's cast untyped values in the weak mode manner, use the "official" rules of validations and type conversions in PHP world!
+    - No need to invent and learn new rules every day every night everywhere.
+    - If the "official" rules doesn't fit your needs, then define ans use your own rules selectively there.
+- If you've ever read [the accepted RFC of STH](https://wiki.php.net/rfc/scalar_type_hints_v5), you would notice the use of weak mode like this library has been already mentioned [there](https://wiki.php.net/rfc/scalar_type_hints_v5#this_proposal_is_a_compromise).
+    > This proposal is not a compromise. It is an attempt of allowing strict typing to work in PHP. A mechanism to bridge untyped PHP code with strict typed PHP code, a “weak” bridge, would be required (otherwise explicit (type) casts would be needed). This proposal unifies the strict and weak typing into a single system that integrates tightly and behaves consistently.  
+
 ## LICENSE
 MIT