[Version 10.0] Feature support for improved definite assignment - #1545
[Version 10.0] Feature support for improved definite assignment#1545RexJaeschke wants to merge 5 commits into
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RexJaeschke
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type: feature
| An expression *E* is said to ***directly contain*** a subexpression *E₁* if it is not subject to a user-defined conversion [§10.5](conversions.md#105-user-defined-conversions) whose parameter is not of a non-nullable value type, and one of the following conditions holds: | ||
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| - *E* is *E₁*. | ||
| - If *E* is a parenthesized expression `(E₂)`, and *E₂* directly contains *E₁*. | ||
| - If *E* is a null-forgiving operator expression `E₂!`, and *E₂* directly contains *E₁*. | ||
| - If *E* is a cast expression `(T)E₂`, and the cast does not subject *E₂* to a non-lifted user-defined conversion whose parameter is not of a non-nullable value type, and *E₂* directly contains *E₁*. | ||
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The MS proposal had this text in the new section, 9.4.4.3x ?.expressions, but as this text is general, and not specific to that expression form, I thought it did not belong there. Short of creating a new section just for this text, I put it in 12.1. Is that OK?
| - The definite-assignment state of *v* before *expr_second* is the same as the definite-assignment state of *v* after *expr_first*. | ||
| - The definite-assignment statement of *v* after *expr* is determined by: | ||
| - If *expr_first* is a constant expression ([§12.26](expressions.md#1226-constant-expressions)) with value `null`, then the state of *v* after *expr* is the same as the state of *v* after *expr_second*. | ||
| - If *expr_first* directly contains ([§12.1](expressions.md#121-general)) a null-conditional expression *E*, and *v* is definitely assigned after the non-conditional counterpart *E₀* (§qdot-expressions), then the definite assignment state of *v* after *expr* is the same as the definite assignment state of *v* after *expr_second*. |
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The instructions in the MS spec for including the new bullet are unclear. They appear to suggest adding the new bullet at the end of the level-2 bullet list. However, that would make it come after the currently final “Otherwise” bullet, which doesn’t seem right. So, I inserted the new bullet before that bullet. Please check if that makes sense.
| - If the state of *v* after *expr_true* is “definitely assigned when true,” and the state of *v* after *expr_false* is “definitely assigned when true,” then the state of *v* after *expr* is “definitely assigned when true.” | ||
| - If the state of *v* after *expr_true* is “definitely assigned when false,” and the state of *v* after *expr_false* is “definitely assigned when false,” then the state of *v* after *expr* is “definitely assigned when false.” |
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The instructions in the MS spec for including the new bullets are unclear. They appear to suggest adding the new bullets at the end of the level-2 bullet list. However, that would make them come after the currently final “Otherwise” bullet, which doesn’t seem right. But that’s where I put them. Please check if that makes sense.
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| > *end note* | ||
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| #### §isop-ispattern-expressions is operator and is pattern expressions |
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I'm curious how this differs from 9.4.4.34 (is pattern expression). Should these two clauses be merged? If not, we need text explaining why they are different.
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An earlier version of this feature is already present on |
`=> null` should be `=> default` in `S2` example because `S2` is a struct. Remove extra `)` from example note Change *null* to `null` add cross references hyphenate "definite-assignment" state
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This is Rex's adaptation of the corresponding MS proposal.