Item 15: Avoid creating unnecessary objects

[rjmurillo]

Related: BillWagner/EffectiveCSharpAnalyzers#15

Style
This may be hard to find, It's looking for member fields that are new'ed up twice in a constructor path.
The most likely case is initialization and ctor.

Creating and destroying heap-based objects is expensive, and doing so unnecessarily in frequently called methods can lead to significant performance degradation. This is particularly problematic in scenarios such as painting operations or string concatenations, where objects may be created and discarded rapidly, leading to excessive pressure on the garbage collector (GC). The .NET Framework provides mechanisms to avoid unnecessary allocations, but it’s crucial to be mindful of these practices when writing code.

One common issue is the creation of objects like fonts, brushes, and strings in methods that are invoked frequently, such as in the OnPaint event handler. Creating a new object each time the method is called causes the GC to work harder, cleaning up these objects after they are no longer in use. This not only slows down your application but also introduces inefficiencies that could easily be avoided.

Examples

OnPaint event handler

protected override void OnPaint(PaintEventArgs e)
{
    // Bad: Created the same font every paint event.
    using (Font myFont = new Font("Arial", 10.0f))
    {
        e.Graphics.DrawString(DateTime.Now.ToString(),
                              myFont,
                              Brushes.Black,
                              new PointF(0, 0));
    }
    base.OnPaint(e);
}

Issue: Every time OnPaint is called, a new Font object is created and then discarded.

String Concatenation

string msg = "Hello, ";
msg += thisUser.Name;
msg += ". Today is ";
msg += DateTime.Now.ToString();

Issue: Each += operation creates a new string object, leading to multiple unnecessary allocations. The pattern is inefficient and can be avoided by using string.Format, StringBuilder, or interpolated strings.

For further details, see #28