Add Flags Attribute concept exercise - #1387
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I'm currently away, so I don't have time to review this right now. Regarding your question: I'm positive that we have other exercises that have the same problem. Likely the discriminated unions exercises. Maybe you could check to see if that is referenced somewhere? There might be an exclude list or something. |
Unlike enum cases in C#, discriminated union members cannot reference other members in F#.
| failwith "Please implement this function" | ||
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| /// Return a set of human-readable phrases indicating the meaning of the given result value. | ||
| let getStatusPhrases (result: Result<string, PasswordError>) : Set<string> = |
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This is returning a Set, which means that the student has to know about sets. So either it needs to be a prerequisite, or we should use a list here (which is my preference).
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OK, I'll modify it to return a list.
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I feel that there might be a more idiomatic F# solution here without using mutable. I'll try and come up with one/
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I think you're right -- probably some kind of map/filter combination. I will also try to come up with something.
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| ## 3. Implement the ``getStatusPhrases` function | ||
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| The `getStatusPhrases` function returns a set of strings each containing a human-readable phrase corresponding to one of the erorrs in the result returned from `checkPassword`. |
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As mentioned elsewhere, I'd suggest making this a simple list.
| - Must have at least one digit | ||
| - Must have at least one symbol in the set !@#$%^&\* | ||
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| Your solution must use a `Result` to encapsulate the success or failure status. |
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These instructions are specific to task 2 (the other tasks don't use results), so should probably be moved to that task (and I've already added some alternative text there).
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It might be worth adding a mention that flags can be set or unset using bitwise operators.
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It's already mentioned on line 20. Do you think additional verbiage is needed?
| [<Fact>] | ||
| [<Task(2)>] | ||
| let ``Missing symbol error with twelve mixed-case letters and digits`` () = | ||
| let expected: Result<string, PasswordError> = Error PasswordError.MissingSymbol | ||
| checkPassword "ABCDEF123ghi" |> should equal expected | ||
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| [<Fact>] | ||
| [<Task(2)>] | ||
| let ``Missing digit error with twelve mixed-case letters and symbols`` () = | ||
| let expected: Result<string, PasswordError> = Error PasswordError.MissingDigit | ||
| checkPassword "ABCDEF$&*ghi" |> should equal expected |
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I would start with these two tests, as that allows the student to first focus on the error-returning bit, and then build on that to add the flag setting pattern to combine values. In other words: if the student would follow the current order, these tests will likely always pass without having to do any work.
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When writing the tests, I had intended to start with the simplest test case first. After looking at it again, I think I got it backwards -- for this exercise, the simplest test case would actually be one in which an Ok result is expected, the next simplest would be one that violates a single rule, the next simplest would be one that violates two rules, etc. I will reorder them.
Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>
- Return a list instead of a set from getStatusPhrases - Order the checkPassword tests from simple to complex - Make the exemplar more idiomatic
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Introduce the Flags Attribute (aka flags-discriminated-union) concept and provide an exercise to teach it. The exercise goal is to use the Flags attribute to build a password checker capable of reporting multiple rule violations in one call.