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c#.netprimitive

.NET primitives and type hierarchies, why was it designed like this?

I would like to understand why on .NET there are nine integer types: Char, Byte, SByte, Int16, UInt16, Int32, UInt32, Int64, and UInt64; plus other numeric types: Single, Double, Decimal; and all these types have no relation at all.

When I first started coding in C# I thought "cool, there's a uint type, I'm going to use that when negative values are not allowed". Then I realized no API used uint but int instead, and that uint is not derived from int, so a conversion was needed.

What are the real world application of these types? Why not have, instead, integer and positiveInteger ? These are types I can understand. A person's age in years is a positiveInteger, and since positiveInteger is a subset of integer there's so need for conversion whenever integer is expected.

The following is a diagram of the type hierarchy in XPath 2.0 and XQuery 1.0. If you look under xs:anyAtomicType you can see the numeric hierarchy decimal > integer > long > int > short > byte. Why wasn't .NET designed like this? Will the new framework "Oslo" be any different?

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Solution

  • My guess would be because the underlying hardware breaks that class hierarchy. There are (perhaps surprisingly) many times when you care that a UInt32 is a 4 bytes big and unsigned, so a UInt32 is not a kind of Int32, nor is an Int32 a type of Int64.

    And you almost always care about the difference between an int and a float.

    Fundamentally, inheritance & the class hierarchy are not the same as mathematical set inclusion. The fact that the values a UInt32 can hold are a strict subset of the values an Int64 can hold does not mean that a UInt32 is a type of Int64. Less obviously, an Int32 is not a type of Int64 - even though there's no conceptual difference between them, their underlying representations are different (4 bytes versus 8 bytes). Decimals are even more different.

    XPath is different: the representations for all the numeric types are fundamentally the same - a string of ASCII digits. There, the difference between a short and a long is one of possible range rather than representation - "123" is both a valid representation of a short and a valid representation of a long with the same value.