Help needed to convert function to a generic function

[Jim Taylor]

I have a function that a function that takes in a string like "1,2,3,4324,3423". I need to return an array of a type that I specifiy using that string so in this case it would return an array of ints or shorts etc like { 1, 2, 3, 4324, 3423 }. The code I wrote to do this is below ... usage: int[] myInts = (int[])CommaSeparatedStringToIEnumerable("1,2,3,4324,3423", typeof(int)); public static IEnumerable CommaSeparatedStringToIEnumerable(string str, Type destinationType) { List list = new List(str.Split(',')); list.RemoveAll(delegate(string s) { return s.Trim().Length == 0 ;}); IEnumerable output; if (destinationType == typeof(int)) output = list.ConvertAll(delegate(string s) { return Convert.ToInt32(s.Trim()); }).ToArray(); else if (destinationType == typeof(short)) output = list.ConvertAll(delegate(string s) { return Convert.ToInt16(s.Trim()); }).ToArray(); else if (destinationType == typeof(byte)) output = list.ConvertAll(delegate(string s) { return Convert.ToByte(s.Trim()); }).ToArray(); else if (destinationType == typeof(bool)) output = list.ConvertAll(delegate(string s) { return Convert.ToBoolean(s.Trim()); }).ToArray(); else if (destinationType == typeof(string)) output = list.ConvertAll(delegate(string s) { return s.Trim(); }).ToArray(); else throw new NotSupportedException("Type not supported."); return output; } I can't help thinking that this could be acheived using a generic function like public static T[] CommaSeparatedStringToArray(string str) but I've been round the houses trying to do this. Any ideas, good articles would be appreciated.

Jim

[Not Active]

static T[] CommaSeparatedStringToIEnumerable(string values) { List list = new List(values.Split(',')); List ret = new List(); foreach(string value in list) ret.Add(ConvertValue(value)); return ret.ToArray(); } static T ConvertValue(object value) { Converter convert = new Converter(delegate(object val) { return (T)val; }); switch(typeof(T).ToString()) { case "System.Int16": case "System.Int32": int RetInt; if(int.TryParse(value.ToString(), out RetInt)) return convert(RetInt); break; case "System.Single": float RetFloat; if(float.TryParse(value.ToString(), out RetFloat)) return convert(RetFloat); break; case "System.Double": double RetDouble; if(double.TryParse(value.ToString(), out RetDouble)) return convert(RetDouble); break; default: return convert(value); } return convert(value); }

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only two letters away from being an asset

[Jim Taylor]

Many thanks Mark, that works a treat!! :)

Jim

[Judah Gabriel Himango]

Here's an elegant way to do it with using C# 2's yield iterators, generics, and delegate inference:

public static IEnumerable<T> CommaSeperatedToIEnumerable<T>(string commaSeperatedValues, Converter<string, T> converter)
{
foreach (string value in commaSeperatedValues.Split(','))
{
yield return converter(value);
}
}

Consuming code would look like this:

IEnumerable<int> myInts = CommaSeperatedSTringToIEnumerable<int>("1,2,3,4324,3423", int.Parse);

Powerful, fun, elegant, works on all types of T. :) Pretty efficient too, since the results will be computed only as you ask for the values in a foreach.

Tech, life, family, faith: Give me a visit. I'm currently blogging about: Funny Love The apostle Paul, modernly speaking: Epistles of Paul Judah Himango

[Jim Taylor]

Thanks Judah that is quite cool. I'm really enjoying learning the new language features in .NET 2.0!

Jim

[Not Active]

Damn, I always forget about the yield keyword, then get reminded, then forget all about it again.

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only two letters away from being an asset

[Judah Gabriel Himango]

The real trick of the above solution, of course, is the Converter<int, T> delegate; without it, we'd have to resort back to the a bunch of if/elses using hard coded types. That's no fun. The yield stuff is really nice. LINQ uses it heavily; you can imagine the LINQ 'where' keyword actually uses a function underneath the hood:

public static IEnumerable<T> Where<T>(IEnumerable<T> items, Predicate<T> criteria)
{
foreach(T item in items)
{
if(criteria(item)) yield return item;
}
}

Of course, with current C# 2 syntax, consuming this is a little ugly:

int[] ints = {5, 10, 15, 20};
IEnumerable evenIntegers = Linq.Where(ints, delegate(int i) { return i % 2 == 0; });

C# 3 makes this a little better with lambda expressions:

IEnumerable evenIntegers = Linq.Where(ints, i => i % 2 == 0);

C# 3 improves it further by extension methods: taking static methods like our Where method and making them appear to be instance methods:

IEnumerable evenIntegers = ints.Where(i => i % 2 == 0);

Better, but still a little odd. The "language integrated" part of LINQ adds some new keywords to C# 3:

IEnumerable evenIntegers = from ints where i % 2 == 0 select i;

Pretty cool stuff; builds heavily on C# 2's delegate inference, anonymous methods, and yielding iterators. And lastly, it's rather laborious to type IEnumerable<int> all over:

var evenIntegers = from ints where i % 2 == 0 select i;

Tech, life, family, faith: Give me a visit. I'm currently blogging about: Funny Love The apostle Paul, modernly speaking: Epistles of Paul Judah Himango

[Nissim Salomon]

Hi the following code use reflection in order to convert string items to value types using the static function TryParse. using System; using System.Collections.Generic; using System.Reflection; namespace CMDLineTest { class Program { static List CommaSeparatedStringToIEnumerable(string s) { List values = new List(); Type targetConversionType = typeof(T); if (targetConversionType.IsValueType) { Type targetConversionTypeOutParamType = Type.GetType(targetConversionType.FullName + @"&"); if(targetConversionTypeOutParamType == null) throw new Exception(""); MethodInfo tryParseMethodInfo = targetConversionType.GetMethod("TryParse", new Type[] { typeof(string), targetConversionTypeOutParamType }); if(tryParseMethodInfo != null) { string[] stringsToConvert = s.Split(','); T item = default(T); object[] methodParams = new object[2]; foreach (string str in stringsToConvert) { methodParams[0] = str; methodParams[1] = item; if (((bool)tryParseMethodInfo.Invoke(null, methodParams)) == true) values.Add((T)methodParams[1]); } } } return values; } static void Main(string[] args) { List intList = CommaSeparatedStringToIEnumerable("1,2,3,4,5"); foreach (int item in intList) Console.WriteLine(item); } } }