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Document SubprocessOutputSequence precondition #352

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Merged
iCharlesHu merged 1 commit into from
Jul 11, 2026
Merged

Document SubprocessOutputSequence precondition #352

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8 changes: 7 additions & 1 deletion Sources/Subprocess/SubprocessOutputSequence.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,9 @@ import os
#endif

/// An asynchronous sequence of buffers that streams output from a subprocess.
///
/// - Important: This sequence is single-pass and can be iterated only once.
/// See ``makeAsyncIterator()``.
public struct SubprocessOutputSequence: AsyncSequence, @unchecked Sendable {
/// The failure type for the asynchronous sequence.
public typealias Failure = any Swift.Error
Expand Down Expand Up @@ -110,9 +113,12 @@ public struct SubprocessOutputSequence: AsyncSequence, @unchecked Sendable {
}

/// Creates an iterator for this asynchronous sequence.
///
/// - Precondition: `SubprocessOutputSequence` is single-pass; creating a
/// second iterator results in a fatal error.
public func makeAsyncIterator() -> Iterator {
guard self.state.initializedCount() == 1 else {
fatalError("SubprocessOutputSequence is single pass. It can only be iterated once.")
fatalError("SubprocessOutputSequence is single-pass. It can only be iterated once.")
}
return Iterator(diskIO: self.diskIO, processIdentifier: self.processIdentifier)
}
Expand Down