🍫 add ABI encoding

solidity/abi_encoding.md

@@ -0,0 +1,24 @@
+## ABI encoding
+
+* the solidity built-in function `abi.encode` encodes solidity types into raw bytes, that can be interpreted directly by the EVM.
+
+
+```
+contract StringEncoding {
+    bytes public encodedString = abi.encode("hacking");
+}
+```
+
+* this is what happens:
+     1. 1st (32 bytes) word = offset → indicates at which bytes index the string starts. If you count 32 from the beginning (= index 32), you will reach the starting point of where the actual encoded string starts.
+     2. 2nd (32 bytes) word = string length → in the case of the string, this indicates how many characters (including whitespaces) are included in the string. 
+     3. 3rd (32 bytes) word = the actual utf8 encoded string → each individual bytes corresponds to hex notation of a letter / character encoded in utf8. 
+
+<br>
+
+#### other ABI Encodings
+
+* address payable -> address
+* contract -> address
+* enum -> uint8
+* struct -> tuple of elementry types