Array sizing

[Neil B]

In C++ arrays have the .SetAtGrow() method that expands the array to
accommodate the index specified. I don't find an equivalent method in C#.

Is there one??

If not, what is the recommended way to handle this??
Currently I'm using the Resize(....) method but this can be awkward at times.

Thanks, Neil

 

[Jeroen Mostert]

In C++ arrays have the .SetAtGrow() method that expands the array to
accommodate the index specified.

You're talking about the MFC CArray class. That's not the same thing as a
"C++ array". C++ has plain old C arrays, but those don't grow.

I don't find an equivalent method in C#.

Is there one??

No. Array objects are immutable in C# (their contents are not, of course).

If not, what is the recommended way to handle this??

Use a List<T> instead. (That's not a linked list, contrary to what you might
think, it's the equivalent of an STL vector.)

List<T> has no way of automatically expanding to a specified index, but it's
easy enough to achieve. Here's an extension method in C# 3 that will achieve
the same as CArray::SetAtGrow:

public static void SetAtGrow<T>(this List<T> list, int index, T item) {
if (list.Count > index) return;
if (list.Capacity < index) list.Capacity = index;
list.AddRange(Forever(default(T)).Take(index - list.Count));
list.Add(item);
}

public static IEnumerable<T> Forever<T>(T item) {
while (true) yield return item;
}

If you're going to do this a lot, you'll want to set .Capacity to a
reasonable value before, to minimize reallocations. If the list you're going

Currently I'm using the Resize(....) method but this can be awkward at times.

I'll say. It'll be especially awkward for performance. .Resize() does not
actually resize an array, it creates a brand new one -- the documentation
explains this.

 

[Ignacio Machin ( .NET/ C# MVP )]

In C++ arrays have the .SetAtGrow() method that expands the array to
accommodate the index specified. I don't find an equivalent method in C#.

Is there one??
No

If not, what is the recommended way to handle this??
Currently I'm using the Resize(....) method but this can be awkward at times.

Thanks, Neil

Use a List<T> collection.

 

[Jeroen Mostert]

public static void SetAtGrow<T>(this List<T> list, int index, T item) {
if (list.Count > index) return;
if (list.Capacity < index) list.Capacity = index;
list.AddRange(Forever(default(T)).Take(index - list.Count));
list.Add(item);
}

Heh. That's what you get for modifying your code halfway through. The
obvious fix:

public static void SetAtGrow<T>(this List<T> list, int index, T newElement) {
if (index < list.Count) {
list[index] = newElement;
return;
}
if (list.Capacity < index) list.Capacity = index;
list.AddRange(Forever(default(T)).Take(index - list.Count));
list.Add(newElement);
}

 

[Jeroen Mostert]

public static void SetAtGrow<T>(this List<T> list, int index, T item) {
if (list.Count > index) return;
if (list.Capacity < index) list.Capacity = index;
list.AddRange(Forever(default(T)).Take(index - list.Count));
list.Add(item);
}

Heh. That's what you get for modifying your code halfway through. The
obvious fix:

public static void SetAtGrow<T>(this List<T> list, int index, T
newElement) {
if (index < list.Count) {
list[index] = newElement;
return;
}
if (list.Capacity < index) list.Capacity = index;
list.AddRange(Forever(default(T)).Take(index - list.Count));
list.Add(newElement);
}

*sigh* The above code still contains one more bug, but this one is left as
an exercise to the reader, as I obviously need some refreshments.