重构指南 - 分解复杂判断（Remove Arrowhead Antipattern）

当代码中有多层嵌套时，会降低代码的可读性，对于以后的修改也增加难度，所以我们需要分解复杂的判断并尽快返回。

重构前代码

public class Security
{
    public ISecurityChecker SecurityChecker { get; set; }

    public Security(ISecurityChecker securityChecker)
    {
        SecurityChecker = securityChecker;
    }

    public bool HasAccess(User user, Permission permission, IEnumerable<Permission> exemptions)
    {
        bool hasPermission = false;

        if (user != null)
        {
            if (permission != null)
            {
                if (exemptions.Count() == )
                {
                    if (SecurityChecker.CheckPermission(user, permission) || exemptions.Contains(permission))
                    {
                        hasPermission = true;
                    }
                }
            }
        }

        return hasPermission;
    }
}

重构后代码

public class Security
{
    public ISecurityChecker SecurityChecker { get; set; }

    public Security(ISecurityChecker securityChecker)
    {
        SecurityChecker = securityChecker;
    }

    public bool HasAccess(User user, Permission permission, IEnumerable<Permission> exemptions)
    {
        if (user == null || permission == null)
            return false;

        if (exemptions.Contains(permission))
            return true;

        return SecurityChecker.CheckPermission(user, permission);
    }
}

重构后的代码，大大提高了可读性和以后的可维护性。