perf: enumerate result pages without boxing - #50
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SvgResult and PngResult forwarded GetEnumerator to the list behind their Pages property, which hands its enumerator back as an IEnumerator<T> and so boxes the struct: 80 bytes per pass over an SVG and a PNG result. A struct enumerator, which foreach binds to in preference to the interface, removes that. Both the foreach path and the interface path go through it, so the two agree on how an exhausted or not-yet-started enumerator behaves. Binary-breaking: a return type is part of the method signature and foreach binds to the concrete method, so an assembly compiled against an earlier version has to be recompiled. Source-compatible.
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SvgResultandPngResultforwardedGetEnumerator()to the list behind theirPagesproperty, which hands its enumerator back as anIEnumerator<T>and so boxes the struct: 80 bytes per pass over an SVG and a PNG result. A struct enumerator, whichforeachbinds to in preference to the interface, removes that. Both theforeachpath and the interface path go through it, so the two agree.Adds one public type,
PageEnumerator<T>. It cannot be hidden: a public method may not return a less accessible type.Binary-breaking, and wider than it looks. A return type is part of the method signature and
foreachbinds to the concrete method, so every already-compiledforeachover a result-typed variable throwsMissingMethodExceptionuntil recompiled, not just code that namedIEnumerator<T>itself. Source-compatible; LINQ,Countand the indexer are unaffected. Needs a version bump rather than a patch, and is recorded in RELEASENOTES.Tests: zero allocations across a pass over both result types, which fails at exactly 80 bytes without the change, plus agreement between the struct path, the indexer and LINQ.
58/58 pass, clean on net8/9/10.