go - 匿名结构作为模板中的管道

Question

有没有办法在 a 中执行以下操作html/template？

{{template "mytemplate" struct{Foo1, Foo2 string}{"Bar1", "Bar2"}}}

我的意思是实际上在模板中，就像上面一样。不是通过注册的函数FuncMap返回结构。

我试过了，但很Parse恐慌，请参阅 Playground。也许我只是语法错误？

Answer 1

正如其他人所指出的，这是不可能的。模板在运行时解析，无需 Go 编译器的帮助。因此，允许任意 Go 语法是不可行的（尽管请注意，这并非不可能，因为标准库包含解析 Go 源文本的所有工具，请参阅go/标准库中“前缀”的包）。按照设计理念，复杂的逻辑应该在模板之外。

回到你的例子：

struct{Foo1, Foo2 string}{"Bar1", "Bar2"}

这是一个结构复合文字，模板不支持它，无论是在调用另一个模板时还是在其他地方。

使用自定义“参数”调用另一个模板具有以下语法（引用自text/template：Actions）：

{{template "name" pipeline}}
    The template with the specified name is executed with dot set
    to the value of the pipeline.

TL;博士; 管道可能是一个常量，一个表示某个值的字段或方法的表达式（将调用该方法并使用它的返回值），它可能是对某些“模板内置”函数或自定义注册的调用函数或映射中的值。

管道在哪里：

管道是可能链接的“命令”序列。命令是一个简单的值（参数）或函数或方法调用，可能带有多个参数：

Argument
  The result is the value of evaluating the argument.
.Method [Argument...]
  The method can be alone or the last element of a chain but,
  unlike methods in the middle of a chain, it can take arguments.
  The result is the value of calling the method with the
  arguments:
      dot.Method(Argument1, etc.)
functionName [Argument...]
  The result is the value of calling the function associated
  with the name:
      function(Argument1, etc.)
  Functions and function names are described below.

一个论点是：

参数是一个简单的值，由以下之一表示。

- A boolean, string, character, integer, floating-point, imaginary
  or complex constant in Go syntax. These behave like Go's untyped
  constants. Note that, as in Go, whether a large integer constant
  overflows when assigned or passed to a function can depend on whether
  the host machine's ints are 32 or 64 bits.
- The keyword nil, representing an untyped Go nil.
- The character '.' (period):
  .
  The result is the value of dot.
- A variable name, which is a (possibly empty) alphanumeric string
  preceded by a dollar sign, such as
  $piOver2
  or
  $
  The result is the value of the variable.
  Variables are described below.
- The name of a field of the data, which must be a struct, preceded
  by a period, such as
  .Field
  The result is the value of the field. Field invocations may be
  chained:
    .Field1.Field2
  Fields can also be evaluated on variables, including chaining:
    $x.Field1.Field2
- The name of a key of the data, which must be a map, preceded
  by a period, such as
  .Key
  The result is the map element value indexed by the key.
  Key invocations may be chained and combined with fields to any
  depth:
    .Field1.Key1.Field2.Key2
  Although the key must be an alphanumeric identifier, unlike with
  field names they do not need to start with an upper case letter.
  Keys can also be evaluated on variables, including chaining:
    $x.key1.key2
- The name of a niladic method of the data, preceded by a period,
  such as
  .Method
  The result is the value of invoking the method with dot as the
  receiver, dot.Method(). Such a method must have one return value (of
  any type) or two return values, the second of which is an error.
  If it has two and the returned error is non-nil, execution terminates
  and an error is returned to the caller as the value of Execute.
  Method invocations may be chained and combined with fields and keys
  to any depth:
    .Field1.Key1.Method1.Field2.Key2.Method2
  Methods can also be evaluated on variables, including chaining:
    $x.Method1.Field
- The name of a niladic function, such as
  fun
  The result is the value of invoking the function, fun(). The return
  types and values behave as in methods. Functions and function
  names are described below.
- A parenthesized instance of one the above, for grouping. The result
  may be accessed by a field or map key invocation.
  print (.F1 arg1) (.F2 arg2)
  (.StructValuedMethod "arg").Field

正确的解决方案是注册一个自定义函数，该函数构造您要传递给模板调用的值，正如您在此相关/可能的重复项中所见：Golang pass multiple values from template to template？

另一个半解决方案可能是使用内置函数print或printf函数来连接您要传递的值，但这需要在另一个模板中拆分。