How to assign a default fallback value to a variable

I have a struct of pointers in my app

type body struct {
   A *string
   B *string
}

I want to pass the values of A and B in the body to function, such that if the pointer A is null, pass a default empty string value. Something like:

sampleFunc(ctx,*A||"");
func sampleFunc(ctx Context,count string){
// ......
}

How do I do this?

There is no built-in syntactic sugar for that, just write the code:

count := ""
if myBody.A != nil {
    count = *myBody.A
}
sampleFunc(ctx, count)

If you find yourself writing this block of code often (say: for many separate fields), you can for example create a helper function:

func getOrDefault(val *string, deflt string) string  {
    if val == nil {
        return deflt
    }
    return *val
}
count := getOrDefault(myBody.A, "")
sampleFunc(ctx, count)

Declare a function with your desired logic for computing a value from the pointer. I use generics here so function works with any type.

// Value returns the value the value pointed
// to by p or the empty value when p is nil.
func Value[T any](p *T) T {
	var result T
	if p != nil {
		result = *p
	}
	return result
}

Use like this:

sampleFunc(ctx, Value(A))

APIs with *string fields often provide a helper function for this purpose. For example, the AWS API provides the StringValue function:

sampleFunc(ctx, aws.StringValue(A))