Improve inline variable

[ahdung]

I hope this code work:

if (_companies?.TryGetValue(CompanyName, out var code) is true)
{
    CompanyCode = code; // 'code' not be initialized
}

instead of:

string code = default;
if (_companies?.TryGetValue(CompanyName, out code) is true)
{
    CompanyCode = code;
}

or

if (_companies != null && _companies.TryGetValue(CompanyName, out var code))
{
    CompanyCode = code;
}

[jnm2]

I do, too. This is tracked at #916 and @333fred has expressed interest in championing it: #3365 (comment)

Oh, more recently, a spec change has been proposed by @RikkiGibson at #4240.

[RikkiGibson]

The goal is to make this happen in C# 10.