首页 \ 问答 \ 习惯性与Rust中的堕落相匹配(Idiomatic match with fall-through in Rust)

习惯性与Rust中的堕落相匹配(Idiomatic match with fall-through in Rust)

 我是Rust的新手，但作为Haskell的粉丝，我非常感谢Rust的match方式。 现在我面临着一个罕见的情况，我确实需要堕落 - 从某种意义上说，我希望所有匹配的几个重叠的案例都能被执行。 这有效：  
fn options(stairs: i32) -> i32 {
    if stairs == 0 {
        return 1;
    }
    let mut count: i32 = 0;
    if stairs >= 1 {
        count += options(stairs - 1);
    }
    if stairs >= 2 {
        count += options(stairs - 2);
    }
    if stairs >= 3 {
        count += options(stairs - 3);
    }
    count
}
 
 我的问题是，这是否是Rust中的惯用语或是否有更好的方法。  
 编辑：上下文是Cracking the Coding Interview的一个问题：“一个孩子正在爬楼梯，有n个步骤，可以一步跳1步，2步或3步。 实施一种方法来计算孩子爬楼梯的可能方式。“ 

I’m new to Rust, but as a fan of Haskell, I greatly appreciate the way match works in Rust. Now I’m faced with the rare case where I do need fall-through – in the sense that I would like all matching cases of several overlapping ones to be executed. This works: 
fn options(stairs: i32) -> i32 {
    if stairs == 0 {
        return 1;
    }
    let mut count: i32 = 0;
    if stairs >= 1 {
        count += options(stairs - 1);
    }
    if stairs >= 2 {
        count += options(stairs - 2);
    }
    if stairs >= 3 {
        count += options(stairs - 3);
    }
    count
}
 
My question is whether this is idiomatic in Rust or whether there is a better way. 
Edit: The context is a question from Cracking the Coding Interview: “A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.”

原文：https://stackoverflow.com/questions/42509526

更新时间：2022-03-23 14:03

最满意答案

 您可以使用CGPDFDocumentCreateWithProvider ：  
 如果你的NSData引用是pdfData那么：  
CFDataRef myPDFData        = (CFDataRef)pdfData;
CGDataProviderRef provider = CGDataProviderCreateWithCFData(myPDFData);
CGPDFDocumentRef pdf       = CGPDFDocumentCreateWithProvider(provider);
 
 但我想你只是想在网页视图中显示它而上述并不是你需要的。  
 但是，如果您已经拥有该URL，则不会更容易存储URL而不是pdf。  
 此外，如果您有数据，可以暂时将其写入文档目录中的文件，然后使用Web视图加载此URL。  
 即;  
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"New1.pdf"];
NSURL *fileURL = [NSURLRequest requestWithURL:appFile];
[data writeToURL:fileURL atomically:YES];
 
 接着 ：  
NSURLRequest *request = [NSURLRequest requestWithURL:fileURL];
[webView loadRequest:request];
 
 如果要从文档目录中删除文件，可以使用：  
[[NSFileManager defaultManager] removeItemAtURL:fileUrl error:nil];
 
 删除您创建的临时pdf。 

You can use CGPDFDocumentCreateWithProvider:  
If your NSData reference is pdfData then: 
CFDataRef myPDFData        = (CFDataRef)pdfData;
CGDataProviderRef provider = CGDataProviderCreateWithCFData(myPDFData);
CGPDFDocumentRef pdf       = CGPDFDocumentCreateWithProvider(provider);
 
But I guess you just want to display it in a web view and the above is not what you need. 
However if you already have the url wouldn't it be easier to store the URL rather than the pdf as such. 
Also if you have the data you can write it into a file inside your documents directory temporarily and then use web view to load this url. 
i.e; 
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"New1.pdf"];
NSURL *fileURL = [NSURLRequest requestWithURL:appFile];
[data writeToURL:fileURL atomically:YES];
 
and then : 
NSURLRequest *request = [NSURLRequest requestWithURL:fileURL];
[webView loadRequest:request];
 
And if you want to remove the file from the documents directory you could use: 
[[NSFileManager defaultManager] removeItemAtURL:fileUrl error:nil];
 
to remove the temporary pdf you created.

习惯性与Rust中的堕落相匹配(Idiomatic match with fall-through in Rust)

最满意答案

相关问答

在Unity中对Json和Json数组进行序列化和反序列化(Serialize and Deserialize Json and Json Array in Unity)[2023-08-22]

如何在Java中序列化和反序列化RSA KeyPair(How to serialize and deserialize a RSA KeyPair in Java)[2022-01-23]

如何在Core Data iOS中序列化和反序列化pdf？(How to serialize and deserialize a pdf in Core Data iOS?)[2023-03-16]

如何对数据库进行序列化和反序列化Perl数据？(How can I serialize and deserialize Perl data to/from database?)[2022-04-03]

DataContractSerializer无法反序列化Net Core 2中的所有属性(DataContractSerializer could not de-serialize all properties in Net Core 2)[2023-04-02]

使用BinaryFormatter序列化和反序列化对象图(Serialize and Deserialize object graph using BinaryFormatter)[2023-12-20]

向量序列化/反序列化中的C ++分段错误(C++ Segmentation Fault in vector serialize/deserialize)[2022-10-27]

FlexiJSon - 序列化反序列化(FlexiJSon - Serialize Deserialize)[2022-05-17]

如何完全序列化/反序列化RSAParameters对象(How to completely serialize/deserialize RSAParameters object)[2022-08-22]

如何使用Woodstox StAX 2序列化/反序列化XML中的类(How do I serialize / deserialize a class in XML with Woodstox StAX 2)[2022-04-19]

相关文章

最新问答