Nemesis.TextParsers 0.11.42

Nemesis.TextParsers

When stucked with a task of parsing various items form strings we ofter opt for TypeConverter (https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.typeconverter) ?

We tend to create methods like:

public static T FromString<T>(string text) =>
    (T)TypeDescriptor.GetConverter(typeof(T))
        .ConvertFromInvariantString(text);

or even create similar constructs to be in line with object oriented design:

public abstract class TextTypeConverter : TypeConverter
{
    public sealed override bool CanConvertFrom(ITypeDescriptorContextcontext, Type sourceType) =>
        sourceType == typeof(string) || base.CanConvertFrom(context, ourceType);

    public sealed override bool CanConvertTo(ITypeDescriptorContext ontext, Type destinationType) =>
        destinationType == typeof(string) || base.CanConvertTocontext, destinationType);
}

public abstract class BaseTextConverter<TValue> : TextTypeConverter
{
    public sealed override object ConvertFrom(ITypeDescriptorContext ontext, CultureInfo culture, object value) =>
        value is string text ? ParseString(text) : default;

    public abstract TValue ParseString(string text);
    

    public sealed override object ConvertTo(ITypeDescriptorContext ontext, CultureInfo culture, object value, Type estinationType) =>
        destinationType == typeof(string) ?
            FormatToString((TValue)value) :
            base.ConvertTo(context, culture, value, destinationType);

    public abstract string FormatToString(TValue value);
}

What is wrong with that? Well, nothing... except of performance.

TypeConverter was designed 15+ years ago when processing power tended to double every now and then and (in my opinion) it was more suited for creating GUI-like editors where performance usually is not an issue. But imagine a service application like exchange trading suite that has to perform multiple operations per second and in such cases processor has more important thing to do than parsing strings.

Parser/formatter features

0. as concise as possible - both JSON or XML exist but thay are not ready to be created from hand by human support
1. works in various architectures supporting .Net Core and .Net Standard and is culture independent
2. support for basic system types (C#-like type names):
   • string
   • bool
   • byte/sbyte
   • short/ushort
   • int/uint
   • long/ulong
   • float/double
   • decimal
   • BigInteger
   • TimeSpan
   • DateTime/DateTimeOffset
   • Guid
3. supports pattern based parsing/formatting via ToString/FromText methods placed inside type or static/instance factory
4. supports compound types:
   • KeyValuePair<,> and ValueTuple of arity 2-5 (1 is not a tuple, more than 5 warrants a dedicated type)
   • Enums (with number underlying types)
   • Nullables
   • Dictionaries (built-in i.e. SortedDictionary/SortedList and custom ones)
   • Arrays (including jagged arrays)
   • Standard collections and collection contracts (List vs IList vs IEnumerable)
   • User defined collections
   • everything mentioned above but combined with inner elements properly escaped in final string i.e. SortedDictionary<char?, IList<float[][]>>
5. ability to fallback to TypeConverter if no parsing/formatting strategy was found
6. parsing is fast to while allocating as little memory as possible upon parsing. The follwing benchmark illustrates this speed via parsing 1000 element array

7. provides basic building blocks for parser's callers to be able to create their own transformers/factories
   • LeanCollection that can store 1,2,3 or more elements
   • string.Split equivalent is provided to accept faster representaion of string - ReadOnlySpan<char>. Supports both standard and custom escaping sequences
   • access to every implemented parser/formatter
8. basic LINQ support

var avg = SpanCollectionSerializer.DefaultInstance.ParseStream<double>("1|2|3".AsSpan()).Average();

9. basic support for GUI editors for compound types like collections/dictionaries
10. lean/frugal implementation of StringBuilder - ValueSequenceBuilder

Span<char> initialBuffer = stackalloc char[32];
var accumulator = new ValueSequenceBuilder<char>initialBuffer);
using (var enumerator = coll.GetEnumerator())
    while (enumerator.MoveNext())
        FormatElement(formatter, enumerator.Current, ref ccumulator);
var text = accumulator.AsSpanTo(accumulator.Length > 0 ? ccumulator.Length - 1 : 0).ToString();
accumulator.Dispose();

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