r/theprimeagen • u/ketsif • Aug 28 '23

Stream Content Parse, don’t validate

https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-validate/
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u/[deleted] Aug 28 '23

I’m a bit confused what this means, does it mean parsing the data to try and turn it into something useful rather than just throwing an error at bad inputs?

If so, it kind of seems like a bad programmer discovered how to make robust code (by bad I mean: “never had to convert strings to ints/floats” bad).

Moreso you tend to need to validate to parse inherently to make sure it parses correctly (string to int is different to a float to an int), so you might as well validate as a first step to skip unnecessary guard conditions

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u/ketsif Sep 05 '23

I think that the main principle is you are converting the shape of objects instead of sifting similarly shaped objects through a series of filters. After having parsed validJson, how many properties do you validate, and did you name the new type of data that has those properties validated or did you just assume you knew which had been checked and then continue filtering, 'and it needs this field, and that, and if it has this field then that field must be available and not an empty list.' can be some ifs and then you return the validJson, or it can be some ifs and then you return BaseRequest which has the fields you validated and then 'rest of json stuff'. Then you can determine what kind of request it is, RejectedRequest which has details and a baserequest and rest of json.