"foo".AsSpan(0, largeNumber) will throw Specified argument was out of the range of valid values. (Parameter 'start').
Note the indicated parameter name. The issue here is the combination of start/length, and there's nothing you can change start to to make this valid as the issue happens to be in the length argument.
We could consider removing the ExceptionArgument.start, or use a different message that doesn't blame start specifically.
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public static ReadOnlySpan<char> AsSpan(this string? text, int start, int length) |
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{ |
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if (text == null) |
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{ |
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if (start != 0 || length != 0) |
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ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start); |
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return default; |
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} |
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#if TARGET_64BIT |
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// See comment in Span<T>.Slice for how this works. |
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if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)text.Length) |
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ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start); |
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#else |
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if ((uint)start > (uint)text.Length || (uint)length > (uint)(text.Length - start)) |
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ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start); |
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#endif |
We don't report the argument in Slice(int, int) for example
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public Span<T> Slice(int start, int length) |
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{ |
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#if TARGET_64BIT |
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// Since start and length are both 32-bit, their sum can be computed across a 64-bit domain |
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// without loss of fidelity. The cast to uint before the cast to ulong ensures that the |
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// extension from 32- to 64-bit is zero-extending rather than sign-extending. The end result |
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// of this is that if either input is negative or if the input sum overflows past Int32.MaxValue, |
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// that information is captured correctly in the comparison against the backing _length field. |
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// We don't use this same mechanism in a 32-bit process due to the overhead of 64-bit arithmetic. |
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if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)_length) |
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ThrowHelper.ThrowArgumentOutOfRangeException(); |
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#else |
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if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start)) |
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ThrowHelper.ThrowArgumentOutOfRangeException(); |
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#endif |
