containers | 易学教程

mutable vs. immutable in Scala collections

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问题 I am fairly new to Scala and am trying to understand the collections hierarchy. I see that there is a distinction between 'mutable' and 'immutable' collections, but I don't understand what this actually means at the implementation level and how this relates to val and var . Can anyone give me some insight on this? Also, does every collection class have a 'mutable' version and an 'immutable' version, or are there some classes which can only be 'mutable' or 'immutable'? 回答1: Mutable means you

Using an IDE while developing on a docker container

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问题 There is something that I am not getting when developing an application while using docker containers. Lets say I am developing a java application and I set up a java container with jdk 8 base image, I still need to install java 8 jdk on my local development machine, since the IDE which I am going to use is going to look for runtime libraries on the local machine not the docker container. Is this right or am I missing something? Somethings I will be able to do entirely on the docker container

What's the difference between std::multimap<key, value> and std::map<key, std::set<value> >

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问题 I found that they have one key and multiple values which is unique. 回答1: The multimap stores pairs of (key, value) where both key and value can appear several times. The map<key, set<value>> will only store each value once for a specific key. To do that, it will have to be able to compare the values, not just the keys. It depends on your application if the values that compare equal are equivalent, or if you wish to store them separately anyway. Perhaps they contain fields that are different

Should custom containers have free begin/end functions?

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问题 When creating a custom container class that plays by the usual rules (i.e. works with STL algorithms, works with well-behaved generic code, etc.), in C++03 it was sufficient to implement iterator support and member begin/end functions. C++11 introduces two new concepts - range-based for loop and std::begin/end. Range-based for loop understands member begin/end functions, so any C++03 containers support range-based for out of the box. For algorithms the recommended way (according to 'Writing

Java EE Containers vs Web Containers

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问题 I'm relatively new to Java EE/EJB, and I've been reading a lot regarding Java EE containers. I've had experience working with a web container (WAR file in JBoss). I am also aware that JBoss can also be used as a Java EE container. What is the difference between a Java EE container against a web container? I know Java EE is also able to contain a .war file. Are they different and what are their differences? Are there any preferences vendor specific-wise which is better? 回答1: First of all,

Why does std::stack use std::deque by default?

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问题 Since the only operations required for a container to be used in a stack are: back() push_back() pop_back() Why is the default container for it a deque instead of a vector? Don't deque reallocations give a buffer of elements before front() so that push_front() is an efficient operation? Aren't these elements wasted since they will never ever be used in the context of a stack? If there is no overhead for using a deque this way instead of a vector, why is the default for priority_queue a vector

Access Container View Controller from Parent iOS

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in iOS6 I noticed the new Container View but am not quite sure how to access it's controller from the containing view. Scenario: I want to access the labels in Alert view controller from the view controller that houses the container view. There's a segue between them, can I use that? Yes, you can use the segue to get access the child view controller (and its view and subviews). Give the segue an identifier (such as alertview_embed ), using the Attributes inspector in Storyboard. Then have the parent view controller (the one housing the container view) implement a method like this: - (void)

When do you prefer using std::list<T> instead of std::vector<T>?

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问题 I've never used std::list<T> myself. I was wondering when people use it when we already have std::vector<T> which is just like arrays with contiguous memory. std::vector seems like a perfect choice when we need sequential container! So my question is When exactly do you prefer std::list over std::vector ? and why exactly? When do you prefer std::vector over std::list ? and why? If there is performance consideration, then please list them too with detail explanation/information. If possible,

Docker in Docker cannot mount volume

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问题 I am running a Jenkins cluster where in the Master and Slave, both are running as a Docker containers. The Host is latest boot2docker VM running on MacOS. To allow Jenkins to be able to perform deployment using Docker, I have mounted the docker.sock and docker client from the host to the Jenkins container like this :- docker run -v /var/run/docker.sock:/var/run/docker.sock -v $(which docker):/usr/bin/docker -v $HOST_JENKINS_DATA_DIRECTORY/jenkins_data:/var/jenkins_home -v $HOST_SSH_KEYS

Standard container re-allocation multipliers across popular toolchains

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问题 Containers like std::basic_string and std::vector perform automatic re-allocations when internal capacity runs out. The standard specifies that, after a re-allocation, .capacity() >= .size() . What are some of the actual multipliers used by mainstream toolchains when performing re-allocations? Update So far, I have: Dinkumware: 1.5 (ships with MSVS and possibly ICC) GNU libstdc++: 2 (ships with GCC and possibly ICC) RW/Apache stdcxx: 1.618 (aka φ) STLport: 2 回答1: New answer for an old