CLSS.Constants.ValueEquivalentStrings 1.1.1

CLSS.Constants.ValueEquivalentStrings

Problem

Among all value types in C#, most of them have equivalent default string representation (as returned by ToString()) if they have equivalent values. This is always the case for built-in value types, this is always the case for enum types, this is always the case for every struct types that can be found in the BCL. The only exception is custom struct types that have custom ToString override and equality conditions that don't align with each other. Those custom structs would create different string content for 2 struct instances that satisfy custom equality conditions.

Since string is a reference type, each ToString invocation always creates an allocation, but since strings are also immutable, there is no real benefit from 2 strings identical in content allocated on 2 different places on the heap. Such a scenario only creates memory inefficiency as well as garbage for the GC to clean up.

string Method1(int value) { return value.ToString(); }
string Method2(int value) { return value.ToString(); }

// These both create "4" strings on the heap at different places in a program
var res1 = Method1(4);
var res2 = Method2(4);

Solution

This package provides the ValueEquivalentStrings<T> class that contains a static, global cache of strings equivalent to value types. The first time it converts a value to a default string (meaning a ToString conversion with no additional format or format provider), it caches that string so that all subsequent conversions simply return that existing string.

int num1 = 4, num2 = 4;
string str1 = ValueEquivalentStrings<int>.Get(num1);
string str2 = ValueEquivalentStrings<int>.Get(num2); // no string allocation for this call

ValueEquivalentStrings accepts all value types in its type parameter, including custom struct types. If you want to cache string equivalences to custom struct types, make sure to align their ToString and Equals override implementations.

using CLSS;

public struct City
{
  public NameEnum Name;
  public CountryEnum Country;
  public static bool operator ==(City lhs, City rhs) => lhs.Equals(rhs);
  public static bool operator !=(City lhs, City rhs) => !lhs.Equals(rhs);
  public override string ToString() => $"(Name = {Name}, Country = {Country})";
  public override bool Equals(object obj)
  {
    if (obj is City otherCity) return this.Name == otherCity.Name;
    return false;
  }
}

// These 2 instances are treated as
// equivalent keys in the Dictionary backing ValueEquivalentStrings.
var paris1 = new City { Name = NameEnum.Paris, Country = CountryEnum.France };
var paris2 = new City { Name = NameEnum.Paris, Country = CountryEnum.USA };
var str1 = ValueEquivalentStrings<City>.Get(paris1);
var str2 = ValueEquivalentStrings<City>.Get(paris2); // returns "(Name = Paris, Country = France)"

At the heart of ValueEquivalentStrings<T> is a MemoizedFunc - another CLSS type and the only dependency of this package. This memoizer is also publicly exposed should you need to manipulate it directly for some reason.

// Invoking the memoizer directly does the same thing as Get, but longer syntax.
char charW = ValueEquivalentStrings<char>.Memoizer.Invoke('W');
// Clears the cache to free up some memory
ValueEquivalentStrings<int>.Memoizer.MemoizedResults.Clear();

This package also comes with the ToCachedString extension method for all value types as an alternative shorter, more functional-style syntax to Get. The same caution for custom struct types applies to this syntax.

// String.Join does not accept char as a separator type in pre-2.1 versions of .NET Standard
var commaSeparatedLine = String.Join(','.ToCachedString(), rowValues);

Note: Since ValueEquivalentStrings<T> is backed by a dictionary, all optimization rules to avoid boxing allocation for a dictionary key type - such as explicit underlying type for enum and implementing IEquatable<T> for struct - also apply to the type parameter of ValueEquivalentStrings<T>.

This package is a part of the C# Language Syntactic Sugar suite.