✨Make QuantityParser public (#1264)

Fixes #1263 

This was initially made internal while we matured its design, but it has
been stable for a long time now and ready for external use. Making it
public makes it possible to parse custom units, as described in the
wiki.

### Changes
- Make `QuantityParser` and its `Parse`, `TryParse` methods public
- Add xmldoc

UnitsNet/CustomCode/QuantityParser.cs

@@ -7,16 +7,24 @@
 using System.Globalization;
 using System.Linq;
 using System.Text.RegularExpressions;
+using UnitsNet.Units;
 
 // ReSharper disable once CheckNamespace
 namespace UnitsNet
 {
-
-    internal delegate TQuantity QuantityFromDelegate<out TQuantity, in TUnitType>(QuantityValue value, TUnitType fromUnit)
+    /// <summary>
+    ///     A method signature for creating a quantity given a numeric value and a strongly typed unit, for example 1.0 and <see cref="LengthUnit.Meter"/>.
+    /// </summary>
+    /// <typeparam name="TQuantity">The type of quantity to create, such as <see cref="Length"/>.</typeparam>
+    /// <typeparam name="TUnitType">The type of unit enum that belongs to this quantity, such as <see cref="LengthUnit"/> for <see cref="Length"/>.</typeparam>
+    public delegate TQuantity QuantityFromDelegate<out TQuantity, in TUnitType>(QuantityValue value, TUnitType fromUnit)
         where TQuantity : IQuantity
         where TUnitType : Enum;
 
-    internal class QuantityParser
+    /// <summary>
+    ///     Parses quantities from strings, such as "1.2 kg" to <see cref="Length"/> or "100 cm" to <see cref="Mass"/>.
+    /// </summary>
+    public class QuantityParser
     {
         /// <summary>
         /// Allow integer, floating point or exponential number formats.
@@ -26,9 +34,17 @@ internal class QuantityParser
         private readonly UnitAbbreviationsCache _unitAbbreviationsCache;
         private readonly UnitParser _unitParser;
 
+        /// <summary>
+        ///     The default instance of <see cref="QuantityParser"/>, which uses <see cref="UnitAbbreviationsCache.Default"/> unit abbreviations.
+        /// </summary>
         public static QuantityParser Default { get; }
 
-        public QuantityParser(UnitAbbreviationsCache? unitAbbreviationsCache)
+        /// <summary>
+        ///     Creates an instance of <see cref="QuantityParser"/>, optionally specifying an <see cref="UnitAbbreviationsCache"/>
+        ///     with unit abbreviations to use when parsing.
+        /// </summary>
+        /// <param name="unitAbbreviationsCache">(Optional) The unit abbreviations cache, or specify <c>null</c> to use <see cref="UnitAbbreviationsCache.Default"/>.</param>
+        public QuantityParser(UnitAbbreviationsCache? unitAbbreviationsCache = null)
         {
             _unitAbbreviationsCache = unitAbbreviationsCache ?? UnitAbbreviationsCache.Default;
             _unitParser = new UnitParser(_unitAbbreviationsCache);
@@ -39,8 +55,19 @@ static QuantityParser()
             Default = new QuantityParser(UnitAbbreviationsCache.Default);
         }
 
+        /// <summary>
+        ///     Parses a quantity from a string, such as "1.2 kg" to <see cref="Length"/> or "100 cm" to <see cref="Mass"/>.
+        /// </summary>
+        /// <param name="str">The string to parse, such as "1.2 kg".</param>
+        /// <param name="formatProvider">The culture for looking up localized unit abbreviations for a language, and for parsing the number formatted in this culture. Defaults to <see cref="CultureInfo.CurrentCulture"/>.</param>
+        /// <param name="fromDelegate">A function to create a quantity given a numeric value and a unit enum value.</param>
+        /// <typeparam name="TQuantity">The type of quantity to create, such as <see cref="Length"/>.</typeparam>
+        /// <typeparam name="TUnitType">The type of unit enum that belongs to this quantity, such as <see cref="LengthUnit"/> for <see cref="Length"/>.</typeparam>
+        /// <returns>The parsed quantity if successful.</returns>
+        /// <exception cref="ArgumentNullException">The string was null.</exception>
+        /// <exception cref="FormatException">Failed to parse quantity.</exception>
         [SuppressMessage("ReSharper", "UseStringInterpolation")]
-        internal TQuantity Parse<TQuantity, TUnitType>(string str,
+        public TQuantity Parse<TQuantity, TUnitType>(string str,
             IFormatProvider? formatProvider,
             QuantityFromDelegate<TQuantity, TUnitType> fromDelegate)
             where TQuantity : IQuantity
@@ -61,8 +88,20 @@ internal TQuantity Parse<TQuantity, TUnitType>(string str,
             return ParseWithRegex(valueString, unitString, fromDelegate, formatProvider);
         }
 
+        /// <summary>
+        ///     Tries to parse a quantity from a string, such as "1.2 kg" to <see cref="Length"/> or "100 cm" to <see cref="Mass"/>.
+        /// </summary>
+        /// <param name="str">The string to parse, such as "1.2 kg".</param>
+        /// <param name="formatProvider">The culture for looking up localized unit abbreviations for a language, and for parsing the number formatted in this culture. Defaults to <see cref="CultureInfo.CurrentCulture"/>.</param>
+        /// <param name="fromDelegate">A function to create a quantity given a numeric value and a unit enum value.</param>
+        /// <param name="result">The parsed quantity if successful, otherwise null.</param>
+        /// <typeparam name="TQuantity">The type of quantity to create, such as <see cref="Length"/>.</typeparam>
+        /// <typeparam name="TUnitType">The type of unit enum that belongs to this quantity, such as <see cref="LengthUnit"/> for <see cref="Length"/>.</typeparam>
+        /// <returns>True if successful.</returns>
+        /// <exception cref="ArgumentNullException">The string was null.</exception>
+        /// <exception cref="FormatException">Failed to parse quantity.</exception>
         [SuppressMessage("ReSharper", "UseStringInterpolation")]
-        internal bool TryParse<TQuantity, TUnitType>(string? str,
+        public bool TryParse<TQuantity, TUnitType>(string? str,
             IFormatProvider? formatProvider,
             QuantityFromDelegate<TQuantity, TUnitType> fromDelegate,
             out TQuantity result)
@@ -81,10 +120,24 @@ internal bool TryParse<TQuantity, TUnitType>(string? str,
         }
 
         /// <summary>
-        ///     Workaround for C# not allowing to pass on 'out' param from type Length to IQuantity, even though the are compatible.
+        ///     Tries to parse a quantity from a string, such as "1.2 kg" to <see cref="Length"/> or "100 cm" to <see cref="Mass"/>.
         /// </summary>
+        /// <remarks>
+        ///     Similar to <see cref="TryParse{TQuantity,TUnitType}(string?,System.IFormatProvider?,UnitsNet.QuantityFromDelegate{TQuantity,TUnitType},out TQuantity)"/>,
+        ///     but returns <see cref="IQuantity"/> instead. This is workaround for C# not allowing to pass on 'out' param from type Length to IQuantity,
+        ///     even though the are compatible.
+        /// </remarks>
+        /// <param name="str">The string to parse, such as "1.2 kg".</param>
+        /// <param name="formatProvider">The culture for looking up localized unit abbreviations for a language, and for parsing the number formatted in this culture. Defaults to <see cref="CultureInfo.CurrentCulture"/>.</param>
+        /// <param name="fromDelegate">A function to create a quantity given a numeric value and a unit enum value.</param>
+        /// <param name="result">The parsed quantity if successful, otherwise null.</param>
+        /// <typeparam name="TQuantity">The type of quantity to create, such as <see cref="Length"/>.</typeparam>
+        /// <typeparam name="TUnitType">The type of unit enum that belongs to this quantity, such as <see cref="LengthUnit"/> for <see cref="Length"/>.</typeparam>
+        /// <returns>True if successful.</returns>
+        /// <exception cref="ArgumentNullException">The string was null.</exception>
+        /// <exception cref="FormatException">Failed to parse quantity.</exception>
         [SuppressMessage("ReSharper", "UseStringInterpolation")]
-        internal bool TryParse<TQuantity, TUnitType>(string str,
+        public bool TryParse<TQuantity, TUnitType>(string str,
             IFormatProvider? formatProvider,
             QuantityFromDelegate<TQuantity, TUnitType> fromDelegate,
             out IQuantity? result)