A property, indexer or dynamic member access may not be passed as an out or ref parameter? [duplicate]

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A property or indexer may not be passed as an out or ref parameter (8 answers)

Closed 8 years ago.

In the code below, I get the error

A property, indexer or dynamic member access may not be passed as an out or ref parameter?

on the m_settings.Lengthargument when compiling it. How could I solve this?

  public override bool Read(GH_IO.Serialization.GH_IReader reader)
                {
                    if (m_settings != null && m_settings.Length > 0)
                    {
                        reader.TryGetInt32("StringCount", ref m_settings.Length);
                        for (int i = 0; i < m_settings.Length; i++)
                        {
                            reader.TryGetString("String", i, ref m_settings[i]);
                        }
                    }
                    return base.Read(reader);
                }

Answer 1

How could I solve this?

By not doing that :) How would you expect it to work anyway? Assuming m_settings is an array, an array can't change length anyway...

If you really need ref behaviour, you'll need a local variable:

int length = m_settings.Length;
reader.TryGetInt32("StringCount", ref length);

// Presumably you want to use length here...
// Perhaps m_settings = new string[length];  ?

It's frankly a little odd that:

• TryGetInt32 uses a ref parameter instead of an out parameter, unlike the normal TryXXX pattern
• You're ignoring the return value of TryGetInt32, which I'd expect to be a success/failure value. Why would you want to silently ignore failure?

Answer 2

Use a temporary local variable:

int temp = 0;
if (reader.TryGetInt32("StringCount", ref temp)) {
    m_settings.Length = temp;
}

Of course this still leaves open some questions:

• you don't check the return value of TryGetInt32 -- what if the conversion fails?
• is m.settings.Length really writeable?