Result (而非恐 慌) 處理這種情況？ /// An operation to perform on two subexpressions. enum Operation { Add, Sub, Mul, Div, } /// An expression, in tree form. enum Expression { /// An operation on two subexpressions let term2 = Expression::Op { op: Operation::Mul, left: Box::new(Expression::Op { op: Operation::Sub, left: Box::new(Expression::Value(3)), right: Box::new(Expression::Value(4)), }), right: Box::new zero")) ); } 12.4.1 解決方案 /// An operation to perform on two subexpressions. enum Operation { Add, Sub, Mul, Div, } /// An expression, in tree form. enum Expression { /// An operation on two subexpressions

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required Consider module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required Consider module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic

as an infix Kronecker product). Operators can also be suffixed with modifying marks, primes, and sub/superscripts, e.g. +̂ₐ″ is parsed as an infix operator with the same precedence as +. A space is required module TestPackage export x, y x = 0 module Sub using ..TestPackage z = y # ERROR: UndefVarError: `y` not defined in `Main` end y = 1 end where Sub is trying to use TestPackage.y before it was defined modification time truncated to the nearest second (to accommodate systems that can't copy mtime with sub-second accuracy). It also takes into account whether the path to the file chosen by the search logic