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[SR-7177] Strange error when calling popFirst() on Array #49725

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swift-ci opened this issue Mar 12, 2018 · 5 comments
Closed

[SR-7177] Strange error when calling popFirst() on Array #49725

swift-ci opened this issue Mar 12, 2018 · 5 comments
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@mdiep
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-7177
Radar rdar://problem/38394649
Original Reporter helge (JIRA User)
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee @mdiep
Priority Medium

md5: 2f3c4a9aee6e8a169df6c551de2bf8e3

Issue Description:

Welcome to Apple Swift version 4.0.3 (swiftlang-900.0.74.1 clang-900.0.39.2). Type :help for assistance.
  1> var a = [ 1,2,3,4 ]
a: [Int] = 4 values {
  [0] = 1
  [1] = 2
  [2] = 3
  [3] = 4
}
  2> a.popFirst()
error: repl.swift:2:1: error: cannot use mutating member on immutable value: 'a' is immutable
a.popFirst()
^

I don't know, but something is going wrong here. `a` is obviously mutable.
@belkadan
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@swift-ci create

@swift-ci
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Comment by Fred Riss (JIRA)

> cat arr.swift
var a = [1,2,3,4]
var b = a.popFirst()
Locals-iMac-Pro-3:/tmp > swiftc -g -Onone arr.swift
arr.swift:2:9: error: cannot use mutating member on immutable value: 'a' is immutable
var b = a.popFirst()
^

It does seem to me odd that a is not considered a mutable array, but it's not special to the REPL.

@belkadan
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Ah, it's just a completely wrong diagnostic. Thanks, Fred.

@mdiep
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mdiep commented Jun 5, 2018

This now gives the correct diagnostic:

error: '[Int]' requires the types '[Int]' and 'ArraySlice<Int>' be equivalent to use 'popFirst'
var b = a.popFirst()
          ^

Although that would ideally explain that popFirst is defined in an extension where SubSequence == Self.

@mdiep
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mdiep commented Jul 6, 2018

The diagnostic has been improved in #17210

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@mdiep mdiep

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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@mdiep @belkadan @swift-ci