Swift Error Handling For Methods That Do Not Throw

'catch' block is unreachable because no errors are thrown in 'do' block
swift catch (nsexception)
no calls to throwing functions occur within 'try' expression
call can throw, but it is not marked with 'try' and the error is not handled
swift print(error)
swift error code
swift rethrow error
try-catch swift stack overflow

This question already has answers here:

Faced with an exception thrown from a method which cannot throw. Found out this exception was thrown from objective-c part of API. So you should catch it in old style way using objective-c.

Firstly create objective-c class which takes several blocks in init method - for try, catch and finally.

#import <Foundation/Foundation.h>

/**
 Simple class for catching Objective-c-style exceptions
 */
@interface ObjcTry : NSObject

/**
 *  Initializeer
 *
 *  @param tryBlock
 *  @param catchBlock
 *  @param finallyBlock
 *
 *  @return object
 */
- (_Nonnull id)initWithTry:(nonnull void(^)(void))tryBlock catch:(nonnull void(^)( NSException * _Nonnull exception))catchBlock finally:(nullable void(^)(void))finallyBlock;

@end

In .m file:

#import "ObjcTry.h"

@implementation ObjcTry

- (_Nonnull id)initWithTry:(nonnull void(^)(void))tryBlock catch:(nonnull void(^)( NSException * _Nonnull exception))catchBlock finally:(nullable void(^)(void))finallyBlock
{
    self = [super init];
    if (self) {
        @try {
            tryBlock ? tryBlock() : nil;
        }
        @catch (NSException *exception) {
            catchBlock ? catchBlock(exception) : nil;
        }
        @finally {
            finallyBlock ? finallyBlock() : nil;
        }
    }
    return self;
}

@end

Second, add its headers to the Bridging Header file.

#import "ObjcTry.h"

And use it in your swift code like that:

var list: [MyModel]!
_ = ObjcTry(withTry: {
    // this method throws but not marked so, you cannot even catch this kind of exception using swift method.
    if let items = NSKeyedUnarchiver.unarchiveObject(with: data) as? [MyModel] {
         list = items
    }
}, catch: { (exception: NSException) in
    print("Could not deserialize models.")
}, finally: nil)

Error Handling — The Swift Programming Language (Swift 5.3), Error handling is the process of responding to and recovering from error Objective-C—error handling in Swift does not involve unwinding the call stack, To indicate that a function, method, or initializer can throw an error, you write the � Error handling in Swift resembles exception handling in other languages, with the use of the try, catch and throw keywords. Unlike exception handling in many languages—including Objective-C—error handling in Swift does not involve unwinding the call stack, a process that can be computationally expensive.

Try catch throw: implementing Error Handling in Swift, Learn how to implement try catch and throwing methods. userIdentifier: String) { // This method is not throwing any errors } func update(name:� Before you can throw an error, you need to make a list of all the possible errors you want to throw. In our case, we're going to stop people from providing empty passwords, short passwords and obvious passwords, but you can extend it later.

I suspect that you'd like to catch errors which is not explicitly marked with "throws".

This makes no sense. You cannot catch other than errors which is explicitly marked with "throws". So, this warning is valid.

For this example, if executed, fatal error: Index out of range will occur. This is runtime error, and you cannot catch it.

For this example, you should check elements size like this, instead of doing try-catch error handling:

Error handling in Swift: try, catch, do and throw, That method is going to encrypt an string using the password that gets sent in. Well, it's not actually going to do that – this article isn't about� Try catch throw: implementing Error Handling in Swift Try catch in Swift combined with throwing errors make it possible to nicely handle any failures in your code. A method can be defined as throwing which basically means that if anything goes wrong, it can throw an error. To catch this error, we need to implement a so-called do-catch statement.

There is a difference between ERRORS and EXCEPTIONS. Swift deals only with errors which are explicitly THROWN and has no native capability for dealing with EXCEPTIONS. As others have commented ERRORS must be thrown and you can't catch what isn't thrown.

By contrast Objective-C @try-@catch deals with exceptions, not errors,. Some objc methods may cause exceptions but do not declare them in any way to the compiler. e.g. FileHandle.write. Such exceptions are more closely aligned to Java's RuntimeException which also does not need to be declared.

There are some situations such as file handling where it would be nice to handle exceptions cleanly in Swift and it is possible by using an Objective-C wrapper. See http://stackoverflow.com/questions/34956002/how-to-properly-handle-nsfilehandle-exceptions-in-swift-2-0

Code reproduced here:

#ifndef ExceptionCatcher_h
#define ExceptionCatcher_h

#import <Foundation/Foundation.h>

NS_INLINE NSException * _Nullable tryBlock(void(^_Nonnull tryBlock)(void)) {
    @try {
        tryBlock();
    }
    @catch (NSException *exception) {
        return exception;
    }
    return nil;
}

#endif /* ExceptionCatcher_h */

Then calling it from Swift:

let exception = tryBlock {
   // execute dangerous code, e.g. write to a file handle
   filehandle.write(data)
}

if exception != nil {
   // deal with exception which is of type NSException
}

Swift 5 Try Catch Syntax and Error Handling (Code Examples), Doing this will completely disregard the fact that an error might be thrown by the method and if an error actually occurs and you don't have the do catch blocks,� Swift Try Catch When you’re coding, you’ll see methods that have the throws keyword. This indicates that the method may raise an error and as a best practice, you should gracefully handle the error and show an appropriate error message to the user. If you don’t catch the error, then your app will crash!

As others mentioned, you should not catch these errors, you should fix them, but in case you want to execute more code before the program terminates, use NSSetUncaughtExceptionHandler in AppDelegate in applicationdidFinishLaunchingWithOptions function.

The function description:

Changes the top-level error handler.

Sets the top-level error-handling function where you can perform last-minute logging before the program terminates.

Error handling in swift. Error handling is the process of…, I will try to explain every aspects of error handling here in this article. There are a number of ways this task can fail, including the file not existing at docs: To indicate that a function, method, or initializer can throw an error,� Swift has first-class support for error handling with the do - try - catch block of code. “First-class” in this case means that do - try - catch has the same kind of control over your app as if and return, for example. With do - try - catch you can handle errors that have been thrown with throw. We’ll get into this syntax later on.

Swift Error handling - Swift try, do catch, throws, Swift does not support checked exceptions. Swift Error Protocol. Error Protocol is just a type for representing error values that can be thrown. Swift� In Swift, contrary to Java, do-catch block is used to handle errors in place of try-catch. Every function that has throws needs to set in the try statement since it has a potential error. Swift try statement is executed only when it is inside the do-catch block as shown below.

Error Handling in Swift, Don't feel disheartened by this though. doSomething() method is not annotated with the throws keyword. Exceptions vs. traditional error-handling methods. Traditionally, a language's error-handling model relied on either the language's unique way of detecting errors and locating handlers for them, or on the error-handling mechanism provided by the operating system. The way .NET implements exception handling provides the following advantages:

Understanding, Preventing and Handling Errors in Swift, method throws the appropriate error if the student attempting to enroll in a course does not meet the minimum achievement level� Throw an InvalidOperationException exception if a property set or method call is not appropriate given the object's current state. Throw an ArgumentException exception or one of the predefined classes that derive from ArgumentException if invalid parameters are passed. End exception class names with the word Exception

Comments

If there is no explicit throw then there is nothing to catch. What's the point of do/catch if there's nothing being thrown?
Well, just because a method does not explicitly "throw" does not mean that a run-time error will not occur :)
It means there is no catchable error. You can't catch uncatchable runtime errors.
Java has uncatchable exceptions (errors). Swift is no different.
@AlexVPerl It's not a bad design decision – fatal errors at runtime shouldn't be caught, as they indicate a programmer error (such as accessing an index out of bounds for a collection or force unwrapping nil). You shouldn't catch such errors, you should fix your code so that they don't occur in the first place.
Swift or ios can behave unexpected even on non-risky functions. There is no preventive measure in swift for unexpected behaviours and this is due to immaturity.
lol the answer is almost the same as the selected one