我来回答第一个问题。以下是Delphi联机帮助的解释，type的用法：
A type declaration specifies an identifier that denotes a type. The syntax for a type declaration is
type newTypeName = type
where newTypeName is a valid identifier. For example, given the type declaration
type TMyString = string;
you can make the variable declaration
var S: TMyString;
A type identifier's scope doesn't include the type declaration itself (except for pointer types). So you cannot, for example, define a record type that uses itself recursively.
When you declare a type that is identical to an existing type, the compiler treats the new type identifier as an alias for the old one. Thus, given the declarations
type TValue = Real;
var
X: Real;
Y: TValue;
X and Y are of the same type; at runtime, there is no way to distinguish TValue from Real. This is usually of little consequence, but if your purpose in defining a new type is to utilize runtime type information--for example, to associate a property editor with properties of a particular type--the distinction between "different name" and "different type" becomes important. In this case, use the syntax
type newTypeName = type type
For example,
type TValue = type Real;
forces the compiler to create a new, distinct type called TValue.
For var parameters, types of formal and actual must be identical. For example,
type
TMyType = type Integer
procedure p(var t:TMyType);
begin end;
procedure x;
var
m: TMyType;
i: Integer;
begin
p(m); //Works
p(i); //Error! Types of formal and actual must be identical.
end;
Note
This only applies to var parameters, not to const or by-value parameters.
他解释清了type mytype = type 与 type mytype = type type的区别。我怕翻译的不好所以贴上原文。
