First draft

Author: matheusaaguiar

_posts/2023-02-08-mapping-named-parameters.md

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+---
+layout: post
+published: true
+title: 'Mapping Named Parameters'
+date: '2023-02-08'
+author: Matheus Aguiar
+category: Explainers
+---
+
+### Intro
+[Solidity 0.8.18](https://github.com/ethereum/solidity/releases/tag/v0.8.18) introduced a language feature that
+was well received by many in the community: Mapping types now have named parameters.
+This new feature opens the possibility to name one or more of the parameters, as we show in the following example.
+
+Example 1:
+
+```solidity
+mapping(string user => uint256 balance) public balanceOf;
+mapping(address key => string) public dictionary;
+
+```
+Notice that the naming of parameters is optional and unnamed mapping declarations are still valid in the language.
+It is particularly useful in situations where there are nested mappings, such as the one presented in the next example.
+
+
+Example 2: (Nested mappings)
+
+```solidity
+
+mapping(address owner => mapping(address spender => uint256 balance)) public allowance;
+
+```
+### Advantages
+
+Tooling can get more info in the generated code.
+TODO: Elaborate on the example of https://github.com/ethereum/solidity/issues/11407 bellow
+
+```
+// solidity
+mapping(address => mapping(address => uint256)) public allowance;
+
+// typescript
+// generated typing
+allowance(arg0: string, arg1: string, overrides?: CallOverrides): Promise<BigNumber>;
+
+// would be great to instead have
+allowance(spender: string, owner: string, overrides?: CallOverrides): Promise<BigNumber>;
+
+```
+Code in general is easier to read, which helps not only in maintenance but also makes faster to understand code.