在评估之前设置QScriptValue局部值 [英] Setting QScriptValue-local values prior to evaluating

问题描述

在Qt 4.8中，可以从C ++端设置 QScriptEngine QScriptValue >？

例如，假设我有：

  QScriptEngine发动机; 
 engine.globalObject（）。setProperty（glob，1000）; 
 
 // ???：将loc设置为，例如42. 
 QScriptValue expr1 = engine.evaluate（glob + loc）; 
 qDebug（）<< expr1.toNumber（）; 
 
 // ???：将loc设置为，例如99. 
 QScriptValue expr2 = engine.evaluate（glob + loc）; 
 qDebug（）<< expr2.toNumber（）; 
  

我想要的输出是：

  1042 
 1099 
  

上面的例子的明显的解决方案是使loc全局和设置+相应地重置它，但是为了分散这个问题，这不是我正在寻找的原因。我想要：

• loc为每个的本地 / li>

• 不要通过例如人工修改脚本字符串 cb> c> c> c> 单个 QScriptEngine 。



我真正想到的只有尝试was：

  QScriptValue expr1 = engine.evaluate（glob + loc）; 
 expr1.setProperty（loc，42）; 
 qDebug（）<< expr1.toNumber（）; 
  

但是似乎该值已经由 evaluate code>因此 setProperty（）没有效果（没有惊喜）。

查看 QScriptProgram 希望它提供了一个程序本地环境，但唉。

我查看文档，并将继续查看他们我发布这，但这是我第一次使用 QScriptEngine ，我不得不承认我的大脑变得糊涂，所以我道歉，如果它是在那里，完全明显。我会接受RTFM作为一个有效的答案。

解决方案

我想出来，至少我认为这是最好的办法。关键是 QScriptEngine＃pushContext（） 和 #popContext（）：

  QScriptEngine发动机; 
 engine.globalObject（）。setProperty（glob，1000）; 
 
 QScriptContext * local; 
 
 local = engine.pushContext（）; 
 local-> activationObject（）。setProperty（loc，42）; 
 QScriptValue expr1 = engine.evaluate（glob + loc）; 
 engine.popContext（）; 
 
 qDebug（）<< expr1.toNumber（）; 
 
 local = engine.pushContext（）; 
 local-> activationObject（）。setProperty（loc，99）; 
 QScriptValue expr2 = engine.evaluate（glob + loc）; 
 engine.popContext（）; 
 
 qDebug（）<< expr2.toNumber（）; 
  

只要给定的 QScriptContext 活动的堆栈，所有 QScriptValue 评估将使用它。相同名称的预先存在的变量将被后续上下文覆盖。

注意，我想你必须使 push→所有评价pop atomic，而不是单独的评估，如果你要去多线程和一个引擎。我希望有一个方法可以传递一个上下文到 evaluate（）。

Is it possible, in Qt 4.8, from the C++ side, to set QScriptValue-local values in a QScriptEngine?

For example, let's say I have:

QScriptEngine engine;
engine.globalObject().setProperty("glob", 1000);

// ???: Set loc to, say, 42.
QScriptValue expr1 = engine.evaluate("glob + loc");
qDebug() << expr1.toNumber();

// ???: Set loc to, say, 99.
QScriptValue expr2 = engine.evaluate("glob + loc");
qDebug() << expr2.toNumber();

And I'd like the output of that to be:

1042
1099

The obvious solution to the contrived example above is to just make "loc" global and set + reset it accordingly, but for reasons that distract from this question that's not what I'm looking for. I'd like:

• "loc" to be local to each QScriptValue
• To not artificially modify the script strings by e.g. prepending QString().sprintf("loc = %d;", 42) or whatever to the scripts.
• To only use a single QScriptEngine.

The only thing I could really think of to try was:

QScriptValue expr1 = engine.evaluate("glob + loc");
expr1.setProperty("loc", 42);
qDebug() << expr1.toNumber();

But it seems the value is already fully evaluated by evaluate() and so setProperty() has no effect (no surprise there).

I also had a peek at QScriptProgram hoping it provided a program-local environment but alas.

I am looking at the docs, and will continue to look at them after I post this, but this is the first time I'm using QScriptEngine and I have to admit my brain is turning to mush, so I apologize if it's right there and totally obvious. I will accept RTFM as a valid answer.

解决方案

I figured it out, at least I think this is the best way. The key is QScriptEngine#pushContext() and #popContext():

QScriptEngine engine;
engine.globalObject().setProperty("glob", 1000);

QScriptContext *local;

local = engine.pushContext();
local->activationObject().setProperty("loc", 42);    
QScriptValue expr1 = engine.evaluate("glob + loc");
engine.popContext();

qDebug() << expr1.toNumber();

local = engine.pushContext();
local->activationObject().setProperty("loc", 99);    
QScriptValue expr2 = engine.evaluate("glob + loc");
engine.popContext();

qDebug() << expr2.toNumber();

And as long as a given QScriptContext is active on the stack, all QScriptValue evaluations will use it. Pre-existing variables of the same name will be overridden by subsequent contexts.

The caveat I guess is you have to make push → all evaluations → pop atomic, rather than individual evaluations, if you're going for multiple threads and one engine. I wish there were a way to pass a context to evaluate().

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