Type.Is Nullable Type Rule Clarification

[bgribaudo]

Per https://learn.microsoft.com/en-us/powerquery-m/m-spec-types#type-equivalence-and-compatibility, this function's second parameter should only ever be a nullable primitive type.

This PR adds details about this requirement to the function's docs.

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[Court72]

@DougKlopfenstein

Can you review the proposed changes?

When the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge.

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[ehrenMSFT]

This is not true. By passing a nullable primitive type as the second arg, you can use Type.Is to check for both the nullable and non-nullable version of that type. But that's just one use of the function.

Here's another way it can be used, which doesn't involve nullable types at all:
Type.Is(Int64.Type, type number)

[bgribaudo]

Hi @ehrenMSFT,

Thanks for this feedback.

Here's another way it can be used, which doesn't involve nullable types at all:
Type.Is(Int64.Type, type number)

I'm puzzled. Isn't type number a nullable primitive type (where nullable primitive type = all primitive types + their nullable counterparts)?

In the language spec, operators as and is are described as only accepting "nullable primitive types as their right operand," and Value.Is's second argument is described as accepting "an arbitrary type value as its first and a nullable primitive type value as its second argument." Examples are given like Type.Is(type number, type text) and 1 is number.

[ehrenMSFT]

Not sure about the spec. I'm just basing my comments on how things actually seem to work.

Type.IsNullable(type number) returns false. You'd have to say "type nullable number" to make it nullable.

[bgribaudo]

Thanks, @ehrenMSFT!

Just opened a PR raising the question of how to best address the "nullable primitive type" terminology used in the spec.

[DougKlopfenstein]

@bgribaudo, @ehrenMSFT - has this pull request reached a conclusion? Is it ready to be merged?

[ehrenMSFT]

@bgribaudo, @ehrenMSFT - has this pull request reached a conclusion? Is it ready to be merged?

My feedback above still applies.

[bgribaudo]

@DougKlopfenstein, thanks for checking up on this. This is blocked by #203. (That PR renames a term in the language spec which can then be used here to resolve @ehrenMSFT's feedback.)