如果get函数中不存在键/值对，该如何创建？

Question

I have a get api like the below:

bool GetValue<T>(string key, out T value);

if the value exists, it is returned in value and the function returns true. Otherwise, value is set to default(T) and the function returns false.

Similarly, I have the set api:

bool SetValue<T>(string key, T value);

Therefore, currently I am using this like:

var exists = GetValue<Details>(@"ProductDetails", out var result);
if (!exists)
{
    _details = new Details();
    SetValue(@"ProductDetails", _details);
}
else
{
    _details = result;
}

I want to create a function that does this in a single line. That is, if the value doesn't already exist it creates a new value with the given arguments and stores that.

How can I do this ?

Answer 1

private T GetOrCreate<T>(string tableName)
    where T : new()
{
    T result;

    var exists = GetValue<T>(tableName, out result);
    if (!exists)
    {
        result = new T();
        SetValue(tableName, result);
    }

    return result;
}

Should do it, using a generic constraint to make sure a default constructor exists for T .