Simplifications and trade-offs in .NET nanoFramework

About this document

This document describes the simplifications and trade-offs introduced in .NET nanoFramework when comparing it to the full framework.

Enums

We are oversimplifying enums. They are special classes which basically contain fields which are constants. ECMA-335 allows several simplifications that our CLR takes advantage of. That's made perfectly clear in the standard by this statement in II.14.3 "These restrictions allow a very efficient implementation of enums."

Since there is no real value in storing the value names and the constants they represent we choose not to do it. This saves an entry in the Fields table and the corresponding ones in the signatures table and also in the strings table (for the value name). At minimum, this would cost 8 + 2 + (n) bytes in the PE file. Mostly depending on the size of the string with the names.

Because of this, we don't have support for Enum.GetNames(), Enum.GetValues() and Enum.IsDefined(). But we have HasFlag()!

Notes:

These could be made available, at the expense of increasing the PE size.
For Enum.IsDefined() you can always use a switch instruction in your code to create something similar depending on your use case.
An enum value's ToString() will return the numerical value as a string, not the enum name as is the case for other platforms.

Multidimensional arrays

Because of the underlying complexity and memory usage, multidimensional arrays are not supported. Only jagged arrays. At the end of the day, these are pretty much equivalent, so if you need multidimensional arrays, you just need to adapt your code to what's available.

String.Format and numeric.ToString Functions

.Net nanoFramework supports a subset of the Standard numeric format strings (D/F/G/N/X) and Composite formatting (left and right alignment). It does NOT support any of the Custom numeric format strings. Strings in nanoFramework are all constrained to UTF-8, so there are limits to the characters that can be displayed. The following format specifiers are supported:

Specifier	Examples
D-Decimal	Decimal unit test output
F-Fixed-point	Fixed-point unit test output
G-General	General unit test output
N-Number	Number unit test output
X-Hexadecimal	Hexadecimal unit test output

Generics