Type Conversion

In certain cases, .NET types may differ between serialiser and deserialiser. Understanding these rules allows the graceful evolution of schema over time.

Here we consider the types of:

• complex type properties
• tuple member

Legend:

🌕 always succeeds
🌑 always fails
🌘 depends upon value

Conversions that depend upon the value can not be relied upon unless you know 100% that out-of-range values will not be serialised.

Dasher Conversions

Left column shows the input (serialised) type. Top row shows output (deserialised) types.

	Byte	SByte	Int16	UInt16	Int32	UInt32	Int64	UInt64	Single	Double	Decimal	Boolean	Char	String	Empty	Byte[]	ArraySegment<byte>
Byte		🌘	🌕	🌕	🌕	🌕	🌕	🌕	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
SByte	🌘		🌕	🌘	🌕	🌘	🌕	🌘	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
Int16	🌘	🌘		🌘	🌕	🌘	🌕	🌘	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
UInt16	🌘	🌘	🌘		🌕	🌕	🌕	🌕	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
Int32	🌘	🌘	🌘	🌘		🌘	🌕	🌘	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
UInt32	🌘	🌘	🌘	🌘	🌘		🌕	🌕	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
Int64	🌘	🌘	🌘	🌘	🌘	🌘		🌘	🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
UInt64	🌘	🌘	🌘	🌘	🌘	🌘	🌘		🌑	🌑	🌕	🌑	🌑	🌑	🌑	🌑	🌑
Single	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌕	🌑	🌑	🌑	🌑	🌑	🌑	🌑
Double	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌑	🌑	🌑	🌑	🌑	🌑	🌑
Decimal	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌑	🌘	🌕	🌑	🌑	🌑
Boolean	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌑	🌑	🌑	🌑	🌑
Char	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌘	🌑		🌕	🌑	🌑	🌑
String	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌘	🌑	🌑		🌘	🌘	🌑
Empty	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌑	🌑
Byte[]	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌕
ArraySegment<byte>	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌕

Some observations:

• Widening integral types of the same sign always works.
• Converting signed to unsigned integers never works all the time.
• Converting unsigned to wider signed integral types always works.
• Narrowing integral types only works if the value received fits within the new type.
• float can always widen to double without loss of precision.
• Integral types can always be converted to decimal without loss of precision.
• string can only convert to char if the string has a single character.
• decimal can convert to string as decimal values are encoded as strings during transport anyway. Conversely, string can convert to decimal if the string passes decimal.TryParse.
• byte[] and ArraySegment<byte> are interchangeable.

In general, Dasher takes a very conservative view on conversions, actively enabling them when provably safe to do so. Cases that only work some of the time are artefacts of the MsgPack encoding used. MsgPack messages do contain some type information, but at a more restricted level than the .NET type system.

.NET Conversions

For contrast, here are the results for the same conversions using .NET's System.Convert.ChangeType(object, Type) method.

	Byte	SByte	Int16	UInt16	Int32	UInt32	Int64	UInt64	Single	Double	Decimal	Boolean	Char	String	Empty	Byte[]	ArraySegment<byte>
Byte		🌘	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌑	🌑	🌑
SByte	🌘		🌕	🌘	🌕	🌘	🌕	🌘	🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
Int16	🌘	🌘		🌘	🌕	🌘	🌕	🌘	🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
UInt16	🌘	🌘	🌘		🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌑	🌑	🌑
Int32	🌘	🌘	🌘	🌘		🌘	🌕	🌘	🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
UInt32	🌘	🌘	🌘	🌘	🌘		🌕	🌕	🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
Int64	🌘	🌘	🌘	🌘	🌘	🌘		🌘	🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
UInt64	🌘	🌘	🌘	🌘	🌘	🌘	🌘		🌕	🌕	🌕	🌕	🌘	🌕	🌑	🌑	🌑
Single	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘		🌕	🌘	🌕	🌑	🌕	🌑	🌑	🌑
Double	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌕		🌘	🌕	🌑	🌕	🌑	🌑	🌑
Decimal	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌕	🌕		🌕	🌑	🌕	🌑	🌑	🌑
Boolean	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕	🌕		🌑	🌕	🌑	🌑	🌑
Char	🌘	🌘	🌘	🌕	🌕	🌕	🌕	🌕	🌑	🌑	🌑	🌑		🌕	🌑	🌑	🌑
String	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌘	🌑		🌘	🌘	🌑
Empty	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌕		🌕	🌑
Byte[]	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑		🌑
ArraySegment<byte>	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑	🌑

These built-in conversions introduce policy, conventions and occasional loss of precision. Dasher may extend its conversion capabilities in future. Use the issue tracker for discussion.