How can I satisfy the compiler to eliminate warning 0052?

Question

I have a desire to satisfy compiler 5 warning level. Thus, I have 32 warnings in a single file FS0052. The value was copied to ensure that the original will not be altered by this operation.

I have been following the only SO message that seems to be related to this warning, but since my type is a type provider created by Microsoft, I cannot just go to the mutable field to disable the warning. plus doing something mutable, which really should never be mutated, seems like a crack is not a fix.

examples:

• Nullable .GetValueOrDefault()
• Nullable .ToString()
• Guide .ToString()
• a call to a structure method of any type that I consider

What is the recommended way to deal with this warning from an appropriate functional point of view?

Answer 1

Not sure if you are still interested.

It seems to me that the compiler gives a warning when it is not sure whether the method call is going to destroy the state of the original instance (this should come mainly from any library outside of F #).

An explicit copy of the value into a variable, in my case, often mitigates the warning. For instance:

open System

// generate the warning due to "ToString()"
let DirSeparator = Path.DirectorySeparatorChar.ToString()  

// no warning
let ExplicitCopy = let x = Path.DirectorySeparatorChar in x.ToString()  

let Alternative = sprintf "%c" Path.DirectorySeparatorChar

Answer 2

What is the recommended way to deal with this warning with a proper functional perspective?

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myStruct.someField <- myRecord.SomeField.ToString()

myStruct.someField <- string myRecord.SomeField

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, GetValueOrDefault.

let valueOrDefault (v: 'a Nullable) = if v.HasValue then v.Value else Unchecked.defaultof<'a>

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