Default value on generic predicate as argument

Question

First time question for me :)

I need some way to define a default predicate using a generic on the format

Func<T, bool>

and then use this as a default argument. Something like this:

public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate = (T t) => true)

When i do this i get the compile error:

Default parameter value for 'predicate' must be a compile-time constant

Is there a smooth way of doing this that I am missing or should a make the predicate function nullable and change my function logic accordingly?

Thanks,

thecoop · Accepted Answer · 2011-01-26 12:31:50Z

Default values for method parameters have to be compile-time constants, as the default values are actually copied to all the call sites of the method by the compiler.

You have to use an overload to do this:

public bool Broadcast(byte command, MemoryStream data, bool async) { return Broadcast(command, data, async, t => true); } public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate) { // ... }

Also, there is a specific Predicate<T> delegate in mscorlib which you can use instead. It's the same signature as Func<T, bool>, but it explicitly marks it as a delegate which decides whether an action is performed on instances of T

I´m going with this for the extra information provided about the Predicate<T>

tenfour · Accepted Answer · 2011-01-26 12:31:00Z

3

Make an overload for Broadcast which does not take the last argument.

answered Jan 26, 2011 at 12:31

tenfour

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Comments

Amir Rezaei · Accepted Answer · 2011-02-18 12:49:03Z

2

Try this:

public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate = default(Func<T, bool>))

But I think you have to check for predicate!=null.

answered Feb 18, 2011 at 12:49

Amir Rezaei

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1 Comment

Bakery Over a year ago

In this case i might as well just do public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate = null)

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